Timing advance acquisition method and apparatus

Abstract

This application provides a timing advance acquisition method and apparatus. The method includes a first network device receiving a first message from a second network device, wherein the first message indicates a first TA and includes first information, the first information including one or more of the following: identification information of a first random access preamble and information of a first time-frequency position, or identification information of a first terminal device, or identification information of a first random access preamble and information of a first time-frequency position and identification information of a first terminal device; and the first network device transmitting a first TA to a first terminal device based on the first information. In this method, the first network device can determine that the first TA corresponds to a first terminal device based on information about the terminal device corresponding to the first TA, and transmit the first TA to the first terminal device to improve the accuracy of the TA acquired by the terminal device.

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims the priority of Chinese Patent Application No. 202310532291.8, titled "TIMING ADVANCE ACQUISITION METHOD AND APPARATUS", filed with the China National Intellectual Property Administration on May 11, 2023, and the entire content thereof is incorporated herein by reference.

[0002] This application relates to the field of communication technologies, and particularly to a timing advance acquisition method and apparatus.

Background Art

[0003] In the process of a terminal device performing an L1 and / or L2 layer-triggered mobility (LTM) switch, the terminal device may access the target cell without random access to avoid interruptions caused by random access. For example, the terminal device may send an uplink message to the network device to which the target cell belongs (e.g., the target distributed unit (DU)) using the target cell's uplink grant (UL grant). After receiving the uplink message, the target DU can consider that the terminal device has successfully switched to the target cell. Before sending the uplink message, the terminal device must obtain the target cell's timing advance (TA) to complete uplink synchronization with the target cell. For example, before receiving a switch command from the network device to which the source cell belongs (e.g., the source DU), the terminal device may send a random access preamble to the target DU. After receiving a random access preamble, to avoid interruptions caused by random access, the target DU may transmit the target cell's TA to the source DU via the central unit (CU) without sending a random access response (RAR) carrying the target cell's TA to the terminal device, and the source DU may then transmit a switch command or downlink message carrying the target cell's TA to the terminal device. [Overview of the Initiative]

[0004] However, if multiple terminal devices in the same source DU to which a source cell belongs send multiple identical random access preambles to a target DU, and the target DU calculates multiple different TAs of the target cell and sends these multiple different TAs to the same source DU via the CU, the source DU cannot determine which terminal device corresponds to each target cell's TA, and therefore the TA of the target cell sent to any terminal device may be an incorrect TA of the target cell. In addition, if multiple terminal devices in different source DUs to which a source cell belongs send multiple different random access preambles to a target DU, and the target DU calculates multiple different TAs of the target cell and sends these multiple different TAs to different source DUs via the CU, the CU cannot determine which source DU corresponds to each target cell's TA, and therefore the TA of the target cell sent to any source DU may be an incorrect TA of the target cell. If any terminal device or any source DU receives an incorrect TA of the target cell, the uplink synchronization with the target cell will be incorrect, and switching from the source cell to the target cell will fail. [Means for solving the problem]

[0005] Embodiments of this application provide a timing advance acquisition method and apparatus for improving the accuracy of timing advances acquired by a terminal device in the timing advance of a target cell.

[0006] According to a first embodiment, a timing advance acquisition method is provided. This method may be implemented by a first network device or a chip within the first network device. An example in which the method is implemented by a first network device is used. The first network device is a network device to which the first source cell of a first terminal device belongs. The method includes the following: a first network device is able to receive a first message from a second network device, the second network device is a network device to which at least one candidate cell of a first terminal device belongs, the first message indicates a first timing advance TA, the first message includes first information, the first information includes identification information for a first random access preamble and information regarding a first time-frequency position for transmitting the first random access preamble, or identification information for a first terminal device, or identification information for a first random access preamble and information regarding a first time-frequency position and identification information for a first terminal device; and the first network device is able to transmit a first TA to the first terminal device based on the first information.

[0007] In the aforementioned solution, when the first TA is transmitted to the first network device, the second network device can synchronously transmit first information, which includes information about the terminal device corresponding to the first TA, for example, identification information of the random access preamble transmitted to the second network device by the terminal device corresponding to the first TA (i.e., identification information of the first random access preamble), information about the time-frequency position at which the terminal device corresponding to the first TA transmits the random access preamble to the second network device (i.e., information about the first time-frequency position), and identification information of the terminal device corresponding to the first TA (i.e., identification information of the first terminal device). In this way, the first network device can determine, based on the first information, that the first TA corresponds to the first terminal device and transmit the first TA to the first terminal device to improve the accuracy of the TA obtained by the terminal device.

[0008] In possible implementations, before receiving the first message from the second network device, the first network device may further send a second message to the first terminal device, the second message indicating that the first terminal device is performing uplink synchronization with the second network device, and the second message includes one or more of the following information: identification information for the first random access preamble and information regarding the first time-frequency position, or information regarding the first beam direction used to determine the first time-frequency position.

[0009] In this implementation, the first network device can determine information about resources used by the first terminal device to perform uplink synchronization with the second network device, and can send information about the resources to the first terminal device using a second message, the second message being, for example, identification information of a first random access preamble sent by the first terminal device to the second network device, information about a first time-frequency position at which the first terminal device transmits the first random access preamble to the second network device, or information about a first beam direction corresponding to the information about a first time-frequency position at which the first terminal device transmits the first random access preamble to the second network device. Furthermore, after receiving information about the first TA and the terminal device corresponding to the first TA, the first network device can determine, based on the information about the terminal device corresponding to the first TA, whether the first TA corresponds to the first terminal device, thereby improving the accuracy of the TA acquired by the terminal device.

[0010] In possible implementations, the first network device can determine, based on the first information, that the first TA corresponds to the first terminal device, and the first network device can transmit the first TA to the first terminal device.

[0011] In this implementation, after receiving information about the first TA and the terminal device corresponding to the first TA, the first network device can determine whether the first TA corresponds to the first terminal device based on the information about the terminal device corresponding to the first TA, thereby improving the accuracy of the TA acquired by the terminal device.

[0012] In possible implementations, the information relating to the first time-frequency position includes one or more of the following information: identification information for random access channel occasions, information relating to a temporary identifier for a random access radio network, or system frame number indicating a value of at least one bit of the system frame number.

[0013] By providing one or more of the aforementioned pieces of information, the first network device can quickly learn the time-frequency position at which a terminal device corresponding to the first TA transmits a random access preamble to the second network device, and can further determine whether the first TA corresponds to the first terminal device, thereby improving the accuracy of the TA acquired by the terminal device.

[0014] In a possible implementation, the first information further includes first identification information, the first identification information indicates a first target cell of a first terminal device or a second network device, and the first target cell is one of at least one candidate cell.

[0015] With the aforementioned information provided, the first network device can quickly learn the target cell of the terminal device corresponding to the first TA, or the network device to which the target cell belongs, and determine whether the first TA corresponds to the first terminal device. In this way, even if the source cells of multiple terminal devices belong to the same network device, and the target cells of multiple terminal devices are different, if the network device to which the target cells belong is the same, the network device to which the source cell belongs can determine the terminal device corresponding to the received TA, thereby improving the accuracy of the TA acquired by the terminal device.

[0016] In a possible implementation, before sending a second message to the first terminal device, the first network device may receive a third message from the second network device, the third message indicating a first resource in at least one candidate cell, the first resource being used by the terminal device in the first source cell to perform uplink synchronization with the second network device.

[0017] In this implementation, the first network device can use a third message to determine information about a first resource used by a terminal device in the first source cell to perform uplink synchronization with a second network device. Furthermore, after receiving information about the first TA and the terminal device corresponding to the first TA, the first network device improves the accuracy of the TA obtained by the terminal device by determining whether the first TA corresponds to the first terminal device, depending on whether the information about the terminal device corresponding to the first TA matches the information about the first resource.

[0018] In possible implementations, the first network device may further determine a second resource from the first resource, the second resource being used by the first terminal device to perform uplink synchronization with the second network device, and the information relating to the second resource includes one or more of the following information: identification information of the first random access preamble and information relating to the first time-frequency position, or information relating to the first beam direction.

[0019] In this implementation, the first network device can determine information about a second resource used by a terminal device in a first source cell to perform uplink synchronization with a second network device, based on information about a first resource used by a terminal device in a first source cell to perform uplink synchronization with a second network device. Furthermore, after receiving information about the first TA and the terminal device corresponding to the first TA, the first network device can determine whether the first TA corresponds to the first terminal device, depending on whether the information about the terminal device corresponding to the first TA matches the information about the second resource, thereby improving the accuracy of the TA obtained by the terminal device.

[0020] In a possible implementation, before receiving a third message from the second network device, the first network device may send a fourth message to the second network device, which is used to request the first resource and contains information about the amount of the first resource.

[0021] In this implementation, the second network device can use a fourth message to determine information about the amount of first resources used by terminal devices in the first source cell to perform uplink synchronization with the second network device, thereby ensuring that there is an appropriate amount of resources provided to terminal devices in the first source cell, using resources from at least one candidate cell.

[0022] In possible implementations, the fourth message further includes one or more of the following information: first identification information indicating a first target cell of a first terminal device or a second network device, wherein the first target cell is at least one of the candidate cells; or second identification information indicating a first source cell or a first network device.

[0023] With the aforementioned information provided, the second network device can quickly learn that resources from the first target cell or the second network device need to be provided to or served by the first network device for a terminal device in the first source cell. Furthermore, after receiving a random access preamble from a terminal device in the first source cell, the second network device can determine that the TA obtained by calculation based on the random access preamble corresponds to the terminal device in the first source cell.

[0024] According to a second embodiment, a timing advance acquisition method is provided. This method may be performed by a second network device or a chip within a second network device. An example is used in which the method is performed by a second network device. The second network device is a network device to which at least one candidate cell of the first terminal device belongs. The method includes the following: a second network device can receive a first random access preamble from a first terminal device; and the second network device can send a first message to the first network device, wherein the first network device is the network device to which the first source cell of the first terminal device belongs; the first message indicates a first TA; the first message includes first information, the first information indicates that the first TA corresponds to the first terminal device; and the first information includes identification information for the first random access preamble and information regarding a first time-frequency position for transmitting the first random access preamble, or identification information for the first terminal device, or identification information for the first random access preamble and information regarding a first time-frequency position and identification information for the first terminal device.

[0025] In the foregoing solution, when the first TA is sent to the first network device, the second network device can synchronously send the first information, and the first information includes information about the first terminal device corresponding to the first TA. For example, it includes the identification information of the first random access preamble sent by the first terminal device to the second network device, the information about the first time-frequency position where the first terminal device sends the first random access preamble to the second network device, and the identification information of the first terminal device. In this way, based on the first information, the first network device can determine that the first TA corresponds to the first terminal device, and send the first TA to the first terminal device, thereby improving the accuracy of the TA obtained by the terminal device.

[0026] In a possible implementation form, the information about the first time-frequency position includes one or more of the following information, that is, the identification information of the random access channel occasion, the information about the temporary identifier of the random access wireless network, or the indication information of the system frame number indicating at least 1 bit value of the system frame number.

[0027] By providing one or more of the foregoing information, the first network device can quickly learn the time-frequency position where the terminal device corresponding to the first TA sends the random access preamble to the second network device, determine whether the first TA corresponds to the first terminal device, and improve the accuracy of the TA obtained by the terminal device.

[0028] In a possible implementation form, the first information further includes first identification information, and the first identification information indicates the first target cell of the first terminal device or the second network device, and the first target cell is any one of at least one candidate cell.

[0029] By providing the foregoing information, the first network device can quickly learn the target cell of the terminal device corresponding to the first TA or the network device to which the target cell belongs, and can determine whether the first TA corresponds to the first terminal device. In this way, even if the source cells of multiple terminal devices belong to the same network device and the target cells of multiple terminal devices are different, when the network devices to which the target cells belong are the same, the network device to which the source cell belongs can determine the terminal device corresponding to the received TA, and improve the accuracy of the TA obtained by the terminal device.

[0030] In a possible implementation form, before receiving the first random access preamble from the first terminal device, the second network device can further send a third message to the first network device, and the third message indicates the first resource of at least one candidate cell, and the first resource is used by the terminal device in the first source cell to perform uplink synchronization with the second network device.

[0031] In this implementation form, the first network device can use the third message to determine information about the first resource used by the terminal device in the first source cell to perform uplink synchronization with the second network device. Further, after receiving the information about the first TA and the terminal device corresponding to the first TA, the first network device determines whether the first TA corresponds to the first terminal device according to whether the information about the terminal device corresponding to the first TA matches the information about the first resource, and improves the accuracy of the TA obtained by the terminal device.

[0032] In a possible implementation, before sending a third message to the first network device, the second network device may receive a fourth message from the first network device, which is used to request the first resource and contains information about the amount of the first resource.

[0033] In this implementation, the second network device can use a fourth message to determine information about the amount of first resources used by terminal devices in the first source cell to perform uplink synchronization with the second network device, thereby ensuring that there is an appropriate amount of resources provided to terminal devices in the first source cell, using resources from at least one candidate cell.

[0034] In possible implementations, the fourth message further includes one or more of the following information: first identification information indicating a first target cell of a first terminal device or a second network device, wherein the first target cell is one of at least one candidate cell; or second identification information indicating a first source cell or a first network device.

[0035] With the aforementioned information provided, the second network device can quickly learn that resources from the first target cell or the second network device need to be provided to or served by the first network device for a terminal device in the first source cell. Furthermore, after receiving a random access preamble from a terminal device in the first source cell, the second network device can determine that the TA obtained by calculation based on the random access preamble corresponds to the terminal device in the first source cell.

[0036] In possible implementations, if the first information includes identification information for the first terminal device, the second network device may receive further identification information for the first terminal device from the first terminal device before sending the first message to the first network device.

[0037] In this implementation, the second network device can determine, based on the identification information of the first terminal device, that the first TA obtained by calculation based on the first random access preamble corresponds to the first terminal device, and then synchronously transmit first information when transmitting the first TA to the first network device, the first information including the identification information of the first terminal device, and as a result, the first network device can determine, based on the first information, that the first TA corresponds to the first terminal device, and transmit the first TA to the first terminal device to improve the accuracy of the TA obtained by the terminal device.

[0038] According to a third embodiment, a timing advance acquisition method is provided. This method may be performed by a second network device or a chip within a second network device. An example is used in which the method is performed by a second network device. The second network device is a network device to which at least one candidate cell of the first terminal device belongs. The method includes the following: a second network device being able to receive a first random access preamble from a first terminal device; and the second network device being able to send a fifth message to a third network device, the fifth message indicating a first TA; the fifth message including second information, the second information indicating that the first TA corresponds to a first network device to which the first source cell of the first terminal device belongs; and the second information including identification information for the first random access preamble and information regarding a first time-frequency position for transmitting the first random access preamble, or second identification information indicating a first source cell or a first network device, or identification information for the first random access preamble and information regarding a first time-frequency position and second identification information.

[0039] In the aforementioned solution, when the first TA is transmitted to the third network device, the second network device can synchronously transmit second information, which includes information about the first terminal device corresponding to the first TA, and for example, includes identification information of the first random access preamble transmitted to the second network device by the first terminal device, information about the first time-frequency position at which the first terminal device transmits the first random access preamble to the second network device, and second identification information indicating the first source cell of the first terminal device or the first network device to which the first source cell belongs. In this way, the third network device can determine, based on the second information, that the first TA corresponds to the network device to which the first source cell belongs, and transmit the first TA to the network device to which the first source cell belongs, thereby improving the accuracy of the TA obtained by the network device to which the source cell of the terminal device belongs, and improving the accuracy of the TA obtained by the terminal device.

[0040] In possible implementations, the information relating to the first time-frequency position includes one or more of the following information: identification information for random access channel occasions, or information relating to a temporary identifier for a random access radio network, or system frame number indicating a value of at least one bit of the system frame number.

[0041] By providing one or more of the aforementioned pieces of information, the third network device can quickly learn the time-frequency position at which a terminal device corresponding to the first TA transmits a random access preamble to the second network device, determine whether the first TA corresponds to the network device to which the first source cell of the first terminal device belongs, improve the accuracy of the TA obtained by the network device to which the source cell of the terminal device belongs, and improve the accuracy of the TA obtained by the terminal device.

[0042] In a possible implementation, the second network device may send a sixth message to the third network device before receiving the first random access preamble from the first terminal device, the sixth message indicating a fourth resource of at least one candidate cell, the fourth resource being used by the terminal device in the second source cell of the first source cell and the second terminal device to perform uplink synchronization with the second network device, the network device to which the second source cell belongs being the fourth network device.

[0043] In this implementation, the third network device can use the sixth message to determine information about the first source cell and the fourth resource used by the terminal device in the second source cell to perform uplink synchronization with the second network device. Furthermore, after receiving information about the first TA and the terminal device corresponding to the first TA, the third network device determines whether the first TA corresponds to the network device to which the first source cell of the first terminal device belongs, depending on whether the information about the terminal device corresponding to the first TA matches the information about the fourth resource, thereby improving the accuracy of the TA obtained by the network device to which the first source cell of the terminal device belongs, and improving the accuracy of the TA obtained by the terminal device.

[0044] In a possible implementation, before sending the sixth message to the third network device, the second network device may receive a seventh message from the third network device, which is used to request the fourth resource and contains information about the amount of the fourth resource.

[0045] In this implementation, the second network device can use the seventh message to determine information about the amount of the fourth resource used by the terminal device in the first source cell to perform uplink synchronization with the second network device, thereby ensuring that there is an appropriate amount of resources provided to the terminal devices in the first and second source cells, using resources from at least one candidate cell.

[0046] In a possible implementation, the seventh message further includes one or more of the following information: first identification information indicating a first target cell of a first terminal device or a second network device, wherein the first target cell is one of at least one candidate cell; or second identification information; or third identification information indicating a second target cell of a second terminal device or a second network device, wherein the second target cell is one of at least one candidate cell; or fourth identification information indicating a second source cell.

[0047] With the aforementioned information provided, the second network device can quickly learn that resources from the first target cell or the second network device need to be provided to or serviced by the first network device for terminal devices in the first source cell, and that resources from the second target cell or the second network device need to be provided to terminal devices in the second source cell or the first network device, and the first and second target cells may be the same cell or different cells. Furthermore, after receiving a random access preamble from a terminal device in the first or second source cell, the second network device can determine that the TA obtained by calculation based on the random access preamble corresponds to a terminal device in the first or second source cell.

[0048] In possible implementations, before sending the sixth message to the third network device, the second network device may further determine the first and fifth resources from the fourth resource, the first resource being used by terminal devices in the first source cell to perform uplink synchronization with the second network device, the fifth resource being used by terminal devices in the second source cell to perform uplink synchronization with the second network device, and the first resource being different from the fifth resource.

[0049] In this implementation, the second network device can determine, from information about a fourth resource used by terminal devices in the first source cell to perform uplink synchronization with the second network device, and information about a fifth resource used by terminal devices in the second source cell to perform uplink synchronization with the second network device, based on information about a fourth resource used by terminal devices in the first source cell to perform uplink synchronization with the second network device. Furthermore, after receiving a random access preamble from a terminal device in the first or second source cell, the second network device can determine that the TA obtained by calculation based on the random access preamble corresponds to the network device to which the first or second source cell belongs, thereby improving the accuracy of the TA obtained by the network device to which the source cell of the terminal device belongs, and improving the accuracy of the TA obtained by the terminal device.

[0050] In possible implementations, the second information includes second identification information, and after receiving a first random access preamble from a first terminal device, the second network device can further determine the second identification information based on the first random access preamble and the first resource.

[0051] In this implementation, the second network device, after receiving a random access preamble from the first terminal device, determines that the TA obtained by calculation based on the random access preamble corresponds to the network device to which the first source cell of the first terminal device belongs. This improves the accuracy of the TA obtained by the network device to which the source cell of the terminal device belongs, thereby improving the accuracy of the TA obtained by the terminal device.

[0052] According to a fourth aspect, a timing advance acquisition method is provided. This method may be performed by a third network device or a chip within the third network device. An example in which the method is performed by a third network device is used. The method includes, namely, that the third network device is able to receive a fifth message from a second network device, wherein the second network device is a network device to which at least one candidate cell of a first terminal device belongs, the fifth message indicates a first TA, the fifth message includes second information, the second information includes identification information for a first random access preamble and information regarding a first time-frequency position for transmitting the first random access preamble, or second identification information indicating a first source cell of the first terminal device or a first network device to which the first source cell belongs, or identification information for a first random access preamble and information regarding a first time-frequency position and second identification information, and the third network device is able to send the fifth message to the first network device based on the second information.

[0053] In the aforementioned solution, when transmitting the first TA to the third network device, the second network device can synchronously transmit second information, which includes information about the first terminal device corresponding to the first TA, for example, identification information of the first random access preamble transmitted to the second network device by the first terminal device, information about the first time-frequency position at which the first terminal device transmits the first random access preamble to the second network device, and second identification information indicating the first source cell of the first terminal device or the first network device to which the first source cell belongs. In this way, the third network device can determine, based on the second information, that the first TA corresponds to the first network device to which the first source cell belongs, and transmit the first TA to the first network device to which the first source cell belongs, thereby improving the accuracy of the TA obtained by the network device to which the source cell of the terminal device belongs, and improving the accuracy of the TA obtained by the terminal device.

[0054] In possible implementations, the third network device can determine, based on the second information, that the first TA corresponds to the first network device and send a fifth message to the first network device.

[0055] In this implementation, the third network device determines, based on the second information, that the first TA corresponds to the first network device to which the first source cell belongs, and transmits the first TA to the first network device to which the first source cell belongs, thereby improving the accuracy of the TA acquired by the network device to which the source cell of the terminal device belongs, and improving the accuracy of the TA acquired by the terminal device.

[0056] In possible implementations, the information relating to the first time-frequency position includes one or more of the following information: one or more of the identification information of random access channel occasions, or information relating to a temporary identifier of a random access radio network, or information indicating a system frame number that represents at least one bit of the system frame number.

[0057] By providing one or more of the aforementioned pieces of information, the third network device can quickly learn the time-frequency position at which a terminal device corresponding to the first TA transmits a random access preamble to the second network device, determine whether the first TA corresponds to the first network device to which the first source cell of the first terminal device belongs, improve the accuracy of the TA obtained by the network device to which the source cell of the terminal device belongs, and improve the accuracy of the TA obtained by the terminal device.

[0058] In a possible implementation, before receiving the fifth message from the second network device, the third network device may further receive a sixth message from the second network device, the sixth message indicating a fourth resource in at least one candidate cell, the fourth resource being used by terminal devices in the first source cell and the second terminal devices in the second source cell to perform uplink synchronization with the second network device, the network device to which the second source cell belongs is the fourth network device, the third network device may further determine the first and fifth resources from the fourth resource, the first resource being used by terminal devices in the first source cell to perform uplink synchronization with the second network device, the fifth resource being used by terminal devices in the second source cell to perform uplink synchronization with the second network device, the first resource being different from the fifth resource, and the third network device may further send an eighth message to the first network device, the eighth message indicating the first resource.

[0059] In this implementation, the third network device can determine information about a fourth resource used by terminal devices in the first and second source cells to perform uplink synchronization with the second network device using a sixth message, and can determine information about a first resource used by terminal devices in the first source cell to perform uplink synchronization with the second network device, and information about a fifth resource used by terminal devices in the second source cell to perform uplink synchronization with the second network device, from the information about the fourth resource. Furthermore, after receiving a random access preamble from the first terminal device, the third network device determines that the TA obtained by calculation based on the random access preamble corresponds to the first network device to which the first source cell of the first terminal device belongs, thereby improving the accuracy of the TA obtained by the network device to which the source cell of the terminal device belongs, and improving the accuracy of the TA obtained by the terminal device.

[0060] In a possible implementation, the first resource is a resource corresponding to the first bandwidth portion BWP of at least one candidate cell, and the fifth resource is a resource corresponding to the second BWP of at least one candidate cell.

[0061] In this implementation, the third network device can divide the fourth resource into a first resource and a fifth resource at the cell granularity, so that the BWP corresponding to the resource used by the terminal device in the first source cell to perform uplink synchronization with the second network device is different from the BWP corresponding to the resource used by the terminal device in the second source cell to perform uplink synchronization with the second network device.

[0062] In possible implementations, the second piece of information further includes identification information for the first BWP.

[0063] By providing one or more of the aforementioned pieces of information, the third network device can quickly learn the BWP corresponding to the resources used by the terminal device corresponding to the first TA to perform uplink synchronization with the second network device, determine whether the first TA corresponds to the first network device to which the first source cell of the first terminal device belongs, improve the accuracy of the TA obtained by the network device to which the source cell of the terminal device belongs, and improve the accuracy of the TA obtained by the terminal device.

[0064] In a possible implementation, before receiving the sixth message from the second network device, the third network device may send a seventh message to the second network device, which is used to request the fourth resource and contains information about the amount of the fourth resource.

[0065] In this implementation, the second network device can use the seventh message to determine information about the amount of the fourth resource used by the terminal device in the first source cell to perform uplink synchronization with the second network device, thereby ensuring that there is an appropriate amount of resources provided to the terminal devices in the first and second source cells, using resources from at least one candidate cell.

[0066] In a possible implementation, the seventh message further includes one or more of the following information: first identification information indicating a first target cell of a first terminal device or a second network device, wherein the first target cell is one of at least one candidate cell; or second identification information; or third identification information indicating a second target cell of a second terminal device or a second network device, wherein the second target cell is one of at least one candidate cell; or fourth identification information indicating a second source cell.

[0067] With the aforementioned information provided, the second network device can quickly learn that the resources of the first target cell need to be provided to the terminal device in the first source cell, and that the resources of the second target cell need to be provided to the terminal device in the second source cell, and the first and second target cells may be the same cell or different cells. Furthermore, after receiving a random access preamble from the terminal device in the first or second source cell, the second network device can determine that the TA obtained by calculation based on the random access preamble corresponds to the terminal device in the first or second source cell.

[0068] According to a fifth aspect, a communication device is provided. The device includes a module / unit / technical means configured to perform a method according to any one of the following: the first aspect or a possible implementation of the first aspect, the second aspect or a possible implementation of the second aspect, the third aspect or a possible implementation of the third aspect, or the fourth aspect or a possible implementation of the fourth aspect.

[0069] According to the sixth aspect, a communication device is provided. The communication device includes a processor and an interface circuit. The interface circuit is configured to receive signals from another communication device different from the communication device and transmit them to the processor, or to transmit signals from the processor to another communication device different from the communication device. The processor is configured to implement any one of the methods of the first aspect or a possible implementation of the first aspect, the second aspect or a possible implementation of the second aspect, the third aspect or a possible implementation of the third aspect, or the fourth aspect or a possible implementation of the fourth aspect, either through logic circuits or by executing code instructions.

[0070] Optionally, the communication device may further include memory.

[0071] According to the seventh aspect, a computer-readable storage medium is provided. The computer-readable storage medium includes a program or instructions. When the program or instructions are executed on a computer, a method according to one of the first aspect or a possible implementation of the first aspect, the second aspect or a possible implementation of the second aspect, the third aspect or a possible implementation of the third aspect, or the fourth aspect or a possible implementation of the fourth aspect is performed.

[0072] According to the eighth aspect, a computer program product is provided. The computer program product includes instructions. When the instructions are executed on a computer, a method is performed according to one of the following: the first aspect or a possible implementation of the first aspect, the second aspect or a possible implementation of the second aspect, the third aspect or a possible implementation of the third aspect, or the fourth aspect or a possible implementation of the fourth aspect.

[0073] According to the ninth aspect, a communication system is provided. The communication system includes a device in any one of the fifth aspect or a possible implementation of the fifth aspect. [Brief explanation of the drawing]

[0074] [Figure 1] This is a diagram of the architecture of a communication system according to one embodiment of this application. [Figure 2] This is a diagram of a CU-DU partitioning architecture used by a network device according to one embodiment of the present application. [Figure 3a] This is a schematic flowchart of existing LTM switching. [Figure 3b] This is a schematic flowchart of other existing LTM switching solutions. [Figure 3c] Here is an overview flowchart of other existing LTM switching methods. [Figure 3d] This is a diagram illustrating an LTM switching scenario, as an example in this application. [Figure 3e] This is a diagram illustrating another LTM switching scenario, as an example in this application. [Figure 3f] This is a diagram illustrating yet another LTM switching scenario, as an example in this application. [Figure 3g] This is a diagram illustrating yet another LTM switching scenario, as an example in this application. [Figure 4] This is a schematic flowchart of a timing advance acquisition method according to one embodiment of this application. [Figure 5] This is a schematic flowchart illustrating the acquisition of uplink synchronization resources according to one embodiment of this application. [Figure 6] This figure shows how to obtain identification information of a terminal device according to one embodiment of this application. [Figure 7] This is a schematic flowchart of another timing advance acquisition method according to one embodiment of this application. [Figure 8] This is another schematic flowchart for acquiring uplink synchronization resources according to one embodiment of the present application. [Figure 9] This is yet another schematic flowchart for acquiring uplink synchronization resources according to one embodiment of the present application. [Figure 10] This is a schematic flowchart of yet another timing advance acquisition method according to one embodiment of this application. [Figure 11] This is yet another schematic flowchart for acquiring uplink synchronization resources according to one embodiment of the present application. [Figure 12] This is yet another schematic flowchart for acquiring uplink synchronization resources according to one embodiment of the present application. [Figure 13] This is a diagram showing the structure of a communication device according to one embodiment of the present application. [Figure 14] This is a diagram showing the structure of another communication device according to one embodiment of this application. [Modes for carrying out the invention]

[0075] To further clarify the purpose, technical solutions, and advantages of the embodiments of this application, the embodiments of this application will be described in more detail below with reference to the accompanying drawings.

[0076] The technical solutions in the embodiments of this application may be applied to various communication systems, such as Universal Mobile Telecommunications Systems (UMTS), Code Division Multiple Access (CDMA) systems, Wireless Local Area Networks (WLANs), Sidelink communication systems, 4th generation (4G) communication systems, 5th generation (5G) wireless communication systems, 6th generation (6G) communication systems, or other future development systems, or various other wireless communication systems using wireless access technology. The technical solutions in the embodiments of this application may be used on the condition that the communication system has cell switching requirements.

[0077] Figure 1 is a diagram of the architecture of a communication system according to one embodiment of this application. As shown in Figure 1, the communication system includes a network device and a terminal device.

[0078] Network devices may include base stations, evolved NodeBs (eNodeBs), transmission reception points (TRPs), next-generation NodeBs (gNBs) in 5th generation (5G) mobile communication systems, next-generation base stations in 6th generation (6G) mobile communication systems, base stations in future mobile communication systems, access nodes in WiFi systems, etc., or they may be modules or units that perform some of the functions of a base station, for example, a central unit (CU) or a distributed unit (DU). The CU, as used herein, can perform the functions of the base station's radio resource control (RRC) protocol and packet data convergence protocol (PDCP), and further perform the functions of the service data adaptation protocol (SDAP). The DU can perform the functions of the base station's radio link control (RLC) and medium access control (MAC) layers, and further perform some or all of the functions of the physical (PHY) layer. For a specific description of the protocol layers mentioned above, please refer to the technical specifications related to the 3rd generation partnership project (3GPP). The network device may be a macro base station, a micro base station or indoor base station, or a relay node, donor node, etc. The embodiments of this application are not limited to any particular technology or device form used for the network device.

[0079] In embodiments of this application, a network device may use a CU-DU partitioned architecture. A CU-DU partitioned architecture may also be called a distributed deployment architecture. For example, Figure 2 is a diagram of a CU-DU partitioned architecture used by a network device according to one embodiment of this application. As shown in Figure 2, the network device may logically include one CU and one or more DUs. Each DU may be connected to the CU via an F1 interface. Information exchange between different DUs may be completed based on transfers performed by the CU. The CU and DU may be physically located together or physically located separately; this is not limited. The CU may support RRC, PDCP, and SDAP functionalities. The DU may support RLC layer protocol, MAC layer protocol, and PHY layer protocol functionalities.

[0080] Terminal devices are sometimes also called terminals, user equipment (UE), mobile stations, or mobile terminals. Terminal devices can be widely used in various scenarios, such as device-to-device (D2D), vehicle-to-everything (V2X) communication, machine-type communication (MTC), the Internet of Things (IoT), virtual reality, augmented reality, industrial control, autonomous driving, telemedicine, smart grids, smart furniture, smart offices, smart wearables, smart transportation, and smart cities. Terminal devices may include mobile phones, tablet computers, computers with wireless transceiver capabilities, wearable devices, vehicles, unmanned aerial vehicles, helicopters, airplanes, ships, robots, robotic arms, and smart home devices. The embodiments of this application are not limited to specific technologies or specific device forms used in terminal devices.

[0081] In embodiments of this application, network devices and terminal devices may be in a fixed location or may be mobile. Network devices and terminal devices may be deployed on land, and deployments may include indoor or outdoor, handheld or vehicle-mounted deployments, deployments on water, or deployments on aircraft, balloons, and orbital satellites. In embodiments of this application, the application scenarios for network devices and terminal devices are not limited.

[0082] The roles of network devices and terminal devices can be relative. For example, an unmanned aerial vehicle (UAV) may be configured as a mobile network device. In the case of a terminal device accessing the network via the UAV, the UAV is a network device. However, in the case of a network device accessed by the UAV, the UAV is a terminal device.

[0083] The functions of a network device may, alternatively, be performed by a module (e.g., a chip) within the network device, or by a control subsystem that includes the functions of the network device. The control subsystem that includes the functions of the network device may be a control center in the aforementioned application scenarios such as smart grids, industrial control, smart transportation, and smart cities. The functions of a terminal device may, alternatively, be performed by a module (e.g., a chip or modem) within the terminal device, or by a device that includes the functions of the terminal device.

[0084] In the embodiments of this application, communication between a terminal device and a network device means that the terminal device transmits an uplink signal or uplink information to the network device, in which case the uplink information is carried on an uplink channel, and / or that the network device transmits a downlink signal or downlink information to the terminal device, in which case the downlink information is carried on a downlink channel. In order to communicate with the network device, the terminal device needs to establish a radio connection with a cell controlled by the network device (in other words, the terminal device camps on to a cell controlled by the network device). The cell that establishes a radio connection with the terminal device is called the serving cell of the terminal device (i.e., the cell that serves the terminal device).

[0085] A terminal device may be located within the coverage area of ​​one or more cells (carriers), and one or more cells may serve the terminal device. For example, in the scenario shown in Figure 1, the terminal device is located within the coverage area of ​​cell 1 controlled by network device 1, the coverage area of ​​cell 2 controlled by network device 2, and the coverage area of ​​cell 3 controlled by network device 3. Cells 1, 2, and 3 can all serve the terminal device. Note that Figure 1 uses an example where one network device controls only one cell. In actual applications, one network device can control multiple cells. When there are multiple cells serving a terminal device, the terminal device can operate in a carrier aggregation (CA), dual connectivity (DC), or coordinated multiple points transmission / reception (CoMP) manner, and one or more cells may provide the terminal device with one or more radio resources corresponding to two or more sets of transmission parameters for operation.

[0086] A terminal device can perform serving cell switching due to changes in its mobility and / or cell channel state. The serving cell to which the terminal device first camped on (or the cell from which the terminal device wirelessly disconnected or the cell to which the terminal device switched) is called the source cell, and the cell to which the terminal device newly camped on (or the cell to which the terminal device newly established a wireless connection or the cell to which the terminal device switched) is called the target cell. In other words, when a terminal device performs serving cell switching, it means that the terminal device switches from the source cell to the target cell. A terminal device can camp on to only one cell, or it can camp on to multiple cells simultaneously. Multiple cells may be controlled by the same network device or by different network devices. This is not limited to the embodiments of this application. Correspondingly, when performing serving cell switching, a terminal device can switch to only one serving cell, or it can switch to multiple serving cells simultaneously. This is not limited to the embodiments of this application.

[0087] In addition, when a cell communicates with a terminal device (for example, when a cell sends a downlink signal to a terminal device and / or when a cell receives an uplink signal from a terminal device), it means that the network device to which the cell belongs (for example, the base station controlling the cell) communicates with the terminal device. When cells communicate with each other, for example, when one cell communicates with another cell, if the two cells belong to different network devices (for example, two cells controlled by different base stations), it means that the network device to which one cell belongs communicates with the network device to which the other cell belongs (for example, a message is sent between the two network devices), or, if the two cells belong to the same network device (for example, two cells controlled by the same base station), it means that a functional module within the network device controlling one cell signals or exchanges data with a functional module within the network device controlling the other cell.

[0088] In embodiments of this application, the terms “system” and “network” may be used interchangeably. “Multiple” means two or more. With this in mind, “multiple” may also be understood as “at least two” in embodiments of this application. “At least one” may be understood as one or more, e.g., one, two, or more. For example, “including at least one” means including one, two, or more, and is not limited to what is specifically included. For example, if it includes at least one of A, B, and C, it could include A, B, C, A, and B, A and C, B and C, or A, B, and C. Similarly, the understanding of phrases such as “at least one” is the same. The term “and / or” describes an association relationship between related objects and indicates that three relationships may exist. For example, A and / or B may indicate the following three cases: that only A exists, that both A and B exist, and that only B exists. In addition, the letter “ / ” generally indicates an “or” relationship between related objects.

[0089] Unless otherwise specified, ordinal numbers such as "First" and "Second" used in the embodiments of this application are used to distinguish between multiple subjects and are not used to limit the order, chronological order, priority, or importance of multiple subjects. Furthermore, the designation of "First" and "Second" does not necessarily imply that the subjects are different.

[0090] The system architectures to which the embodiments of this application can be applied and the possible application scenarios are described above. To better understand the technical solutions in the embodiments of this application, the relevant technical features of the embodiments are described below.

[0091] In L1 and / or L2 layer-triggered mobility (LTM) switching in a CU-DU partitioned architecture, L1 is the PHY layer, L2 is the MAC layer, RLC layer, PDCP layer, or SDAP layer, and LTM means that switching-related operations are primarily performed at L1 and / or L2. For example, a terminal device transmits L1 measurement results to a base station via PHY layer control signaling (carried over the physical uplink control channel, PUCCH). The base station's PHY layer reads the L1 measurement results. The base station makes a switching decision based on the L1 measurement results and transmits the switching decision to the terminal device via L1 signaling and / or L2 signaling. L1 signaling and / or L2 signaling may be messages carried over the physical downlink control channel (PDCCH) or MAC control elements (MAC CE).

[0092] Figure 3a is a schematic flowchart of existing LTM switching. As shown in Figure 3a, the source DU (S-DU) is the DU to which the source cell of the UE belongs; that is, the source DU provides the source cell to the UE. The target DU (T-DU) is the DU to which the target cell of the UE belongs; that is, the target DU provides the target cell to the UE. The specific steps for performing cell switching between different DUs belonging to the same CU are as follows:

[0093] Step 1: The CU sends resource configuration information for at least one candidate cell to the UE via the source DU. Step 2: The UE sends the measurement results for the source cell and candidate cell to the source DU. Step 3: The source DU sends a switch command to the UE, sending identification information for the target cell to the UE via L1 signaling and / or L2 signaling, in which case the target cell is one of the at least one candidate cell, and the L1 signaling and / or L2 signaling are still sent over the communication resources of the source cell. Step 4: The UE switches from the source cell to the target cell by performing LTM switching, accesses the target cell using the resource configuration information corresponding to the target cell received in Step 1, and after successful access, initiates communication with the target cell (specifically, communication with the target DU, or communication over the communication resources of the target cell). When accessing the target cell, the UE can access the target cell via random access, but random access can cause interruptions; therefore, the UE can access the target cell without random access. For example, a UE sends an uplink message to the target cell via the target cell's uplink grant (UL grant) (e.g., a physical uplink shared channel, PUSCH). After the target cell receives the uplink message, the UE may be considered to have successfully switched to the target cell.

[0094] However, before a UE can send an uplink message to a target cell via the target cell's uplink grant, it needs to obtain the target cell's timing advance (TA) to complete uplink synchronization (i.e., time-domain synchronization) with the target cell in order to determine the time-domain position for sending the uplink message using the target cell's TA. The UE can obtain the target cell's TA using an early random access channel (RACH) solution and a random access response (RAR) without solution. For example, before receiving a switch command from a source DU, the UE can send a random access preamble (i.e., the first message MSG1 in random access processing) to the target DU, and as a result, the target DU obtains the target cell's TA by calculation based on the random access preamble. After receiving a random access preamble and obtaining the target cell's TA through calculations based on the random access preamble, the target DU can send the target cell's TA to the source DU via the CU without sending a random access response (i.e., the second message MSG2 in the random access process) carrying the target cell's TA to the UE. The source DU can then send a switch command or downlink message to the UE carrying the target cell's TA. Since the target DU does not send a random access response to the UE, the UE does not need to listen for a random access response from the target DU. Thus, interruptions due to random access are avoided.

[0095] Figure 3b is a schematic flowchart of another existing LTM switching process. The steps shown in Figure 3b are as follows:

[0096] Step 1: The CU sends resource configuration information for at least one candidate cell to the UE via the source DU. Step 2: The UE sends the measurement results for the source cell and candidate cell to the source DU. Step 3: The source DU sends an uplink synchronization command (e.g., PDCCH command (order)) to the UE, which instructs the UE to send a random access preamble to the target cell. Step 4: The UE sends a random access preamble to the target DU according to the uplink synchronization command. Step 5: The target DU obtains the TA of the target cell by calculation based on the random access preamble and sends the TA of the target cell to the source DU via the CU. Step 6: The source DU sends a switch command to the UE, which includes the TA of the target cell. Step 7: The UE performs LTM switching to switch from the source cell to the target cell.

[0097] Figure 3c is a schematic flowchart of yet another existing LTM switching process. The steps shown in Figure 3c are as follows:

[0098] Step 1: The CU sends resource configuration information for at least one candidate cell to the UE via the source DU. Step 2: The UE sends the measurement results for the source cell and candidate cell to the source DU. Step 3: The source DU sends an uplink synchronization command (e.g., PDCCH order) to the UE, which instructs the UE to send a random access preamble to the target cell. Step 4: The UE sends a random access preamble to the target DU according to the uplink synchronization command. Step 5A: The target DU obtains the TA of the target cell by calculation based on the random access preamble and sends the TA of the target cell to the source DU via the CU. Step 5B: The source DU sends a downlink message to the UE, which carries the TA of the target cell, and the downlink message may be a random access response or MAC CE. Step 6: The source DU sends a switch command to the UE. Step 7: The UE performs LTM switching to switch from the source cell to the target cell.

[0099] However, in scenarios where multiple UEs need to perform LTM switching to switch from a source cell to a target cell, the source DU to which the source cells of the multiple UEs belong may be the same, or the source DU to which the source cells of the multiple UEs belong may be different.

[0100] If the source cells of multiple UEs belong to the same source DU, then multiple UEs can send multiple identical random access preambles to the target DU because they are assigned to the same source DU by the same target cell and because they use the same resources for uplink synchronization. When the target DU obtains multiple different TAs of the target cell by calculation based on multiple identical random access preambles and sends these multiple different TAs of the target cell to the same source DU via the CU, the source DU cannot determine the UE corresponding to each target cell's TA, so the TA of the target cell sent to any UE may be an incorrect TA of the target cell. As a result, uplink synchronization between any UE and the target cell will be incorrect, and the switch from the source cell to the target cell will fail. For example, Figure 3d is a diagram of an LTM switching scenario according to an example of the present application. As shown in Figure 3d, the source cells of UE1 and UE2 are both cell 1, and the target cells of UE1 and UE2 are both cell 2. The DU to which cell 1 belongs is DU1, in other words, the source DU of UE1 and UE2 is DU1. The DU to which cell 2 belongs is DU2, meaning that the target DU for UE1 and UE2 is DU2. UE1 and UE2 send two identical random access preambles to DU2. DU2, through calculations based on these two identical random access preambles, obtains two different TAs for cell 2, which are TA1 and TA2, respectively, and sends TA1 and TA2 to DU1 via CU. DU1 cannot determine which UE corresponds to TA1 and which UE corresponds to TA2. If the UE corresponding to TA1 must be UE1 and the UE corresponding to TA2 must be UE2, then DU1 may send TA1 to UE2 and TA2 to UE1, resulting in incorrect TAs for cell 2 obtained by UE1 and UE2.

[0101] If the source cells of multiple UEs belong to different source DUs, multiple UEs can send multiple different random access preambles to the target DU because they are assigned to different source DUs by the same target cell and use different resources for uplink synchronization. If the target DU obtains multiple different TAs of the target cell by calculation based on multiple different random access preambles and sends multiple different TAs of the target cell to different source DUs via the CU, the CU cannot determine the source DU corresponding to each target cell's TA, so the TA of the target cell sent to any source DU may be an incorrect TA of the target cell. Consequently, the TA of the target cell sent to any UE by any source DU may be an incorrect TA of the target cell. As a result, uplink synchronization between any UE and the target cell will be incorrect, and switching from the source cell to the target cell will fail. For example, Figure 3e illustrates another LTM switching scenario according to an example of the present application. As shown in Figure 3e, the source cell of UE1 is cell 1, the source cell of UE2 is cell 2, and the target cell of both UE1 and UE2 is cell 3. Cell 1 belongs to DU1, in other words, UE1's source DU is DU1. Cell 2 belongs to DU2, in other words, UE2's source DU is DU2. Cell 3 belongs to DU3, in other words, UE1 and UE2's target DU is DU3. UE1 and UE2 send two different random access preambles to DU2. DU2, through calculations based on the two different random access preambles, obtains two different TAs for cell 2, which are TA1 and TA2, respectively, and sends TA1 and TA2 to CU. CU cannot determine which DU corresponds to TA1 and which DU corresponds to TA2. If the DU corresponding to TA1 must be DU1 and the DU corresponding to TA2 must be DU2, CU may send TA1 to DU2 and TA2 to DU1, resulting in incorrect TAs for cell 2 obtained by DU1 and DU2.

[0102] To solve the aforementioned problems, this application provides a timing advance acquisition method. This method can be applied to scenarios in which multiple terminal devices perform cell switching.

[0103] For example, in Scenario 1, the network device to which the source cell of the first terminal device (e.g., referred to as the first source cell) and the source cell of the second terminal device (e.g., referred to as the second source cell) belong is the first network device, the network device to which at least one candidate cell of the first terminal device and at least one candidate cell of the second terminal device belong is the second network device, the first terminal device switches between the first source cell and the first target cell, the first target cell is one of at least one candidate cell, and the second terminal device switches between the second source cell and the second target cell, the second target cell is one of at least one candidate cell. In Scenario 1, it will be understood that the first source cell and the second source cell may be the same cell or different cells, and the first target cell and the second target cell may be the same cell or different cells. This is not limited to the embodiments of this application.

[0104] If the first and second network devices use a CU-DU partitioning architecture, there is a third network device between the first and second network devices, in other words, the third network device is a network device that transmits messages between the first and second network devices. The first and second network devices may be different DUs belonging to the same CU. For example, the first network device may be the first DU belonging to the first CU, the second network device may be the second DU belonging to the first CU, and the third network device may be the first CU. The first and second network devices may be different DUs that do not belong to the same CU. For example, the first network device may be the first DU belonging to the first CU, the second network device may be the second DU belonging to the second CU, and the third network device may be the first CU and the second CU. This is not limited to the embodiments of this application.

[0105] For example, see Figure 3d. The source cell for both UE1 and UE2 is cell 1, and the target cell for both UE1 and UE2 is cell 2. The DU to which cell 1 belongs is DU1, in other words, the source DU for both UE1 and UE2 is DU1. The DU to which cell 2 belongs is DU2, in other words, the target DU for both UE1 and UE2 is DU2. UE1 can switch between cell 1 and cell 2, and UE2 can switch between cell 1 and cell 2.

[0106] Alternatively, Figure 3f illustrates yet another LTM switching scenario according to an example of this application. As shown in Figure 3f, the source cell for both UE1 and UE2 is cell 1. The target cell for UE1 is cell 2, and the target cell for UE2 is cell 3. The DU to which cell 1 belongs is DU1, in other words, the source DU for UE1 and UE2 is DU1. The DU to which cells 2 and cell 3 belong is DU2, in other words, the target DU for UE1 and UE2 is DU2. UE1 can switch between cell 1 and cell 2, and UE2 can switch between cell 1 and cell 3.

[0107] As another example, in Scenario 2, the network device to which the first source cell belongs is the first network device, the network device to which the second source cell belongs is the fourth network device, the network device to which at least one candidate cell of the first terminal device and at least one candidate cell of the second terminal device belongs is the second network device, the first terminal device switches between the first source cell and the first target cell, the first target cell is any one of at least one candidate cell, and the second terminal device switches between the second source cell and the second target cell, the second target cell is any one of at least one candidate cell. In Scenario 2, it will be understood that the first target cell and the second target cell may be the same cell or different cells. This is not limited to the embodiments of this application.

[0108] When the first, second, and fourth network devices use a CU-DU partitioning architecture, there is a third network device between them; in other words, the third network device is a network device that transmits messages between the first, second, and fourth network devices. The first, second, and fourth network devices may be different DUs belonging to the same CU. For example, the first network device may be the first DU belonging to the first CU, the second network device may be the second DU belonging to the first CU, the fourth network device may be the third DU belonging to the first CU, and the third network device may be the first CU. The first, second, and fourth network devices may be different DUs that do not belong to the same CU. For example, the first network device is a first DU belonging to the first CU, the second network device is a second DU belonging to the second CU, the fourth network device is a third DU belonging to the third CU, and the third network device may be the first CU, the second CU, and the third CU. This is not limited to the embodiments of this application.

[0109] For example, see Figure 3e. The source cell for UE1 is cell 1, and the source cell for UE2 is cell 2. The target cell for both UE1 and UE2 is cell 3. The DU to which cell 1 belongs is DU1, in other words, the source DU for UE1 is DU1. The DU to which cell 2 belongs is DU2, in other words, the source DU for UE2 is DU2. The DU to which cell 3 belongs is DU3, in other words, the target DU for both UE1 and UE2 is DU3. UE1 can switch between cell 1 and cell 3, and UE2 can switch between cell 2 and cell 3.

[0110] As yet another example, in Scenario 3, the network device to which the first source cell belongs is the first network device, the network device to which the second source cell and the source cell of the third terminal device (for example, called the third source cell) belong is the fourth network device, and the network device to which at least one candidate cell of the first terminal device, at least one candidate cell of the second terminal device, and at least one candidate cell of the third terminal device belong is the second network device. The first terminal device switches between the first source cell and the first target cell, and the first target cell is one of at least one candidate cell, the second terminal device switches between the second source cell and the second target cell, and the second target cell is one of at least one candidate cell, and the third terminal device switches between the third source cell and the third target cell, and the third target cell is one of at least one candidate cell. In Scenario 3, it will be understood that the second source cell and the third source cell may be the same cell or different cells, and the first target cell, the second target cell, and the third target cell may be the same cell or different cells. This is not limited to the embodiments of this application.

[0111] For example, Figure 3g is a diagram of yet another LTM switching scenario according to an example of the present application. As shown in Figure 3g, the source cell for UE1 is cell 1, and the source cells for UE2 and UE3 are cell 2. The target cell for UE1, UE2, and UE3 is cell 3. The DU to which cell 1 belongs is DU1, in other words, the source DU for UE1 is DU1. The DU to which cell 2 belongs is DU2, in other words, the source DU for UE2 and UE3 is DU2. The DU to which cell 3 belongs is DU3, in other words, the target DU for UE1, UE2, and UE3 is DU3. UE1 can switch between cell 1 and cell 3, UE2 can switch between cell 2 and cell 3, and UE2 can switch between cell 2 and cell 3.

[0112] According to the timing advance acquisition method provided in this application, if the network device to which the source cells of multiple terminal devices (e.g., the first and second terminal devices in Scenario 1, or the second and third terminal devices in Scenario 3) belong is the same network device, it is guaranteed that the network device to which the source cells of the multiple terminal devices belong (e.g., the first or fourth network device) can determine the terminal device corresponding to each received timing advance. Alternatively, if the network devices to which the source cells of multiple terminal devices (e.g., the first and second terminal devices in Scenario 2, the first and second terminal devices in Scenario 3, or the first and third terminal devices in Scenario 3) belong are different network devices, it is guaranteed that the network device between the network device to which at least one candidate cell of the multiple terminal devices belongs and the network device to which the source cells of the multiple terminal devices belong (e.g., the third network device) can determine the network device to which the source cell of the terminal device corresponding to each received timing advance belongs. Therefore, the timing advance of the target cell, and the accuracy of the timing advance acquired by the terminal device, are improved.

[0113] Furthermore, this application specifically includes three possible technical solutions regarding whether the network device to which the source cells of multiple terminal devices belong is the same network device, or whether the network devices to which the source cells of multiple terminal devices belong are different network devices. For ease of explanation, the three possible technical solutions will be referred to as Solution 1, Solution 2, and Solution 3, respectively. Solutions 1, 2, and 3 will be described separately in detail below. It will be understood that in embodiments of this application, only LTM switching technology is used as an example. The technical solutions in embodiments of this application are also applicable to other switching technologies that access the target cell without random access. In the cell switching scenario in embodiments of this application, it will be understood that before cell switching occurs, the target cell is one of at least one of the candidate cells, and once cell switching occurs, any candidate cell becomes the target cell. In the description of the embodiments of this application, the communication interaction between the terminal device and the candidate cell may also be understood as the communication interaction between the terminal device and the target cell, or the communication interaction between the terminal device and the target cell may also be understood as the communication interaction between the terminal device and the candidate cell, since the candidate cell subsequently becomes the target cell.

[0114] Solution 1 Figure 4 is a schematic flowchart of a timing advance acquisition method according to one embodiment of the present application. The method can be applied to the communication system shown in Figure 1, but is not limited thereto. The method can be applied to Scenario 1 described above, but is not limited thereto. In Scenario 1, the first source cell and the second source cell may be the same cell or different cells, and the first target cell and the second target cell may be the same cell or different cells. This is not limited to this embodiment of the present application. For the sake of clarity, this embodiment of the present application uses an example in which the first source cell and the second source cell are the same cell. Hereinafter, the first source cell and the second source cell will be collectively referred to as the first source cell. The method includes the following steps.

[0115] S401: The first terminal device transmits the first random access preamble to the second network device, and in response, the second network device receives the second random access preamble from the first terminal device. The second terminal device transmits the second random access preamble to the second network device, and in response, the second network device receives the second random access preamble from the second terminal device.

[0116] In this embodiment of the present application, a first terminal device can transmit a first random access preamble to a second network device, and in response, the second network device can receive the first random access preamble from the first terminal device. Similarly, a second terminal device can transmit a second random access preamble to a second network device, and in response, the second network device can receive the second random access preamble from the second terminal device. It will be understood that the first random access preamble and the second random access preamble may be the same random access preamble or different random access preambles. This is not limited to this embodiment of the present application.

[0117] The second network device can further obtain a first TA from the first terminal device by calculation based on a first random access preamble, and obtain a second TA from the second terminal device by calculation based on a second random access preamble.

[0118] For example, if the first target cell and the second target cell are the same cell, then, as shown in Figure 3d, the source cell for both UE1 and UE2 is cell 1, and the target cell for both UE1 and UE2 is cell 2. The DU to which cell 1 belongs is DU1, in other words, the source DU for UE1 and UE2 is DU1. The DU to which cell 2 belongs is DU2, in other words, the target DU for UE1 and UE2 is DU2. UE1 and UE2 send two random access preambles to DU2. DU2, through calculations based on the two random access preambles, obtains two different TAs for cell 2, which are TA1 and TA2, respectively.

[0119] Alternatively, if the first target cell and the second target cell are different cells, as shown in Figure 3f, the source cell for both UE1 and UE2 is cell 1. The target cell for UE1 is cell 2, and the target cell for UE2 is cell 3. The DU to which cell 1 belongs is DU1, in other words, the source DU for UE1 and UE2 is DU1. The DU to which cells 2 and 3 belong is DU2, in other words, the target DU for UE1 and UE2 is DU2. UE1 and UE2 send two random access preambles to DU2. DU2, by calculation based on the two random access preambles, obtains the TA of cell 2 and the TA of cell 3, which are TA1 and TA2, respectively.

[0120] Based on the implementation process in Figure 4, if the first and second network devices use a CU-DU partitioned architecture, in other words, if the first and second network devices are DUs and the third network device is a CU, the steps shown in Figure 5 may be further performed in this application.

[0121] In S501, the first network device can send a first request message (or a fourth message) to the second network device via the third network device, and in response, the second network device can receive the first request message from the first network device via the third network device.

[0122] The first request message may be used to request a first resource in at least one candidate cell. The first resource may be used by terminal devices in the first source cell (e.g., the first terminal device and the second terminal device) to perform uplink synchronization with a second network device. Optionally, the first resource may also be used by terminal devices served by the first network device (e.g., the first terminal device and the second terminal device) to perform uplink synchronization with the second network device.

[0123] For example, information about the first resource may include one or more of the following: identification information for a random access preamble transmitted by a terminal device in the first source cell when the terminal device performs uplink synchronization with a second network device; time-frequency location information for the terminal device in the first source cell transmitting the random access preamble when the terminal device performs uplink synchronization with a second network device; and beam direction information corresponding to the time-frequency location information for the terminal device in the first source cell transmitting the random access preamble when the terminal device performs uplink synchronization with a second network device. It will be understood that the information about the first resource at the granularity of the first source cell may alternatively be at the granularity of the first network device. Specifically, the information relating to the first resource may include one or more of the following information: identification information for a random access preamble transmitted by a terminal device served by the first network device when the terminal device performs uplink synchronization with the second network device; information relating to the time-frequency location to which the terminal device served by the first network device transmits the random access preamble when the terminal device performs uplink synchronization with the second network device; and beam direction information corresponding to the time-frequency location to which the terminal device served by the first network device transmits the random access preamble when the terminal device performs uplink synchronization with the second network device. In this embodiment of the present application, a candidate network device (or referred to as a target network device) (e.g., a second network device) may assign a first resource to each source cell (e.g., a first source cell), or each source network device (e.g., a first network device) may be assigned a first resource. One assigned first resource may be provided by each candidate cell.

[0124] In one implementation, the first request message may include information about the amount of the requested first resource. The number of requested first resources may be obtained by the first network device based on the number of terminal devices in the first source cell or the number of terminal devices, where the number of terminal devices is the number of terminal devices in the first source cell that are configured with candidate cells managed by the second network device. For example, if the first source cell is cell 1, the cell managed by the second network device is cell 2, and the terminal devices in cell 1 include terminal device 1 and terminal device 2, and the terminal devices in cell 1 that are configured with cell 2 as a candidate cell also include terminal device 1 and terminal device 2, then the first network device can obtain the amount of resources used by the terminal devices in cell 1, or used by terminal devices in cell 1 that are configured with cell 2 as a candidate cell to perform uplink synchronization with the second network device, by calculation based on the number of terminal devices in cell 1, or the number of terminal devices in cell 1 that are configured with cell 2 as a candidate cell, and can indicate information regarding the amount of resources used by the terminal devices in cell 1, or used by terminal devices in cell 1 that are configured with cell 2 as a candidate cell to perform uplink synchronization with the second network device, in the first request message sent to the second network device. For example, the amount may be large, medium, or small.

[0125] In other implementations, the first request message may further include one or more of the following information: first identification information indicating a first target cell, and second identification information indicating a first source cell. If the first target cell and the second target cell are different cells, it will be understood that the first request message may further include third identification information indicating the second target cell. If the first source cell and the second source cell are different cells, the first request message may further include fourth identification information indicating the second source cell. For example, if the first source cell is cell 1 and the first target cell is cell 2, the first network device may indicate the identification information for cell 1 and / or cell 2 in the first request message sent to the second network device. The second network device may decide, based on the identification information of cell 1 and the identification information of cell 2, that the first request message is used to request that the resources of cell 2 be allocated to a terminal device in cell 1, thereby causing the terminal device in cell 1 to perform uplink synchronization with cell 2. It will be understood that the first identification information may alternatively indicate the second network device to which the first target cell belongs, the second identification information may alternatively indicate the first network device to which the first source cell belongs, the third identification information may alternatively indicate the second network device to which the second target cell belongs, and the fourth identification information may alternatively indicate the first network device to which the second source cell belongs.

[0126] It will be understood that the first and / or second identification information may be explicitly or implicitly indicated within the first request message. This is not limited to this embodiment of the present application. When the first and / or second identification information is implicitly indicated, there is a correspondence between the CU and DU between the cell identifier and the F1 interface identifier. The CU and DU can determine the corresponding cell identifier based on the F1 interface identifier.

[0127] If the first and second network devices do not use a CU-DU partitioned architecture, it will be understood that the first network device can send the first request message to the second network device without using the third network device, or can send the first request message directly to the second network device. Correspondingly, the second network device can receive the first request message from the second network device without using the third network device, or can receive the first request message directly from the second network device.

[0128] In yet another implementation, the first request message may not need to be initiated by the first network device, but may be initiated directly by the third network device; in other words, the first request message is sent to the second network device by the third network device.

[0129] In yet another implementation, the first request message may be a request message at the terminal device level. For example, the first request message may further include one or more of the following information: identification information for the first terminal device, identification information for the second terminal device, instruction information for requesting a first resource shared by the first and second terminal devices, instruction information for requesting a first resource dedicated to the first terminal device, and instruction information for requesting a first resource dedicated to the second terminal device. In this way, if the first terminal device requires low latency, the second network device can allocate a first resource dedicated to the first terminal device. Therefore, in the subsequent S503, the first network device can quickly select a second resource to be used by the first terminal device to perform early synchronization based on the first resource, and as a result, the first terminal device can quickly complete early TA acquisition and perform switching without random access in order to meet the low latency requirement.

[0130] In S502, the second network device can send a first response message (or third message) to the first network device via the third network device, and in response, the first network device can receive the first response message from the second network device via the third network device.

[0131] The first response message may indicate the first resource.

[0132] In one implementation, the first resource may be different from the third resource of at least one candidate cell, and the third resource is used by a terminal device in at least one candidate cell to perform uplink synchronization with the second network device. For example, if the first source cell is cell 1 and at least one candidate cell is cell 2, when the second network device assigns the resources of cell 2 to a terminal device in cell 1 so that the terminal device in cell 1 can perform uplink synchronization with cell 2, the resources assigned to the terminal device in cell 1 are different from the resources assigned to the terminal device in cell 2, so the terminal device in cell 2 is not affected in accessing cell 2 when the terminal device in cell 1 performs uplink synchronization with cell 2.

[0133] It will be understood that the first and third resources may be random access preambles having different route sequences. For example, in 64 random access preambles, preambles a1, ..., and a64 may be assigned to terminal devices in cell 1, and in 64 other random access preambles, preambles b1, ..., and b64 may be assigned to terminal devices in cell 2. Alternatively, the first and third resources may have different time-frequency positions for transmitting random access preambles. For example, the time-frequency position for transmitting a random access preamble assigned to a terminal device in cell 1 may be time-frequency position 1, and the time-frequency position for transmitting a random access preamble assigned to a terminal device in cell 2 may be time-frequency position 2. This is not limited to this embodiment of the present application.

[0134] If the first and second network devices do not use a CU-DU partitioned architecture, it will be understood that the second network device can directly send the first response message to the first network device without using the third network device. Correspondingly, the first network device can receive the first response message from the second network device without using the third network device, and can also directly receive the first response message from the second network device.

[0135] In S503, the first network device can determine the second resource from the first resource, send a first synchronization instruction message (or second message) to the first terminal device, and send a second synchronization instruction message to the second terminal device. Correspondingly, the first terminal device can receive the first synchronization instruction message from the first network device, and the second terminal device can receive the second synchronization instruction message from the first network device.

[0136] The second resource may be used by the first terminal device to perform uplink synchronization with the second network device.

[0137] For example, information about the second resource may include one or more of the following: identification information for a random access preamble transmitted by the first terminal device when the first terminal device performs uplink synchronization with the second network device (e.g., identification information for the first random access preamble); information about the time-frequency location to which the first terminal device transmits the random access preamble when the first terminal device performs uplink synchronization with the second network device (e.g., information about the first time-frequency location); and beam direction information corresponding to the time-frequency location to which the first terminal device transmits the random access preamble when the first terminal device performs uplink synchronization with the second network device (e.g., information about the first beam direction, which is used by the first terminal device to determine the first time-frequency location).

[0138] For example, the information relating to the first time-frequency position may include one or more of the following information: identification information for a random access channel occasion (RACH occasion, RO), information for a random access-radio network temporary identifier (RA-RNTI), and indication information for a system frame number (SFN) that indicates at least one bit of the system frame number.

[0139] A first synchronization instruction message may instruct a first terminal device to perform uplink synchronization with a second network device.

[0140] For example, the first synchronization instruction message may include one or more of the following information: identification information and information regarding the first time-frequency position of the first random access preamble, and information regarding the first beam direction. In other words, the first synchronization instruction message may include information regarding the second resource.

[0141] A second synchronization instruction message may instruct a second terminal device to perform uplink synchronization with a second network device.

[0142] For example, the second synchronization instruction message may include one or more of the following information: identification information for a second random access preamble transmitted by the second terminal device when the second terminal device performs uplink synchronization with the second network device (e.g., identification information for the second random access preamble); information about the time-frequency location to which the second terminal device transmits the random access preamble when the second terminal device performs uplink synchronization with the second network device (e.g., information about the second time-frequency location); and information about the beam direction corresponding to the time-frequency location to which the second terminal device transmits the random access preamble when the second terminal device performs uplink synchronization with the second network device (e.g., information about the second beam direction, which is used by the second terminal device to determine the second time-frequency location).

[0143] Optionally, in S502 and S503, the first resources configured for the first and second terminal devices may first be transmitted to the first network device by the second network device via the third network device, and then the first network device determines the second resource from the first resource and transmits the second resource to the first terminal device. Example 1 of the first resources configured for the first and second terminal devices is the first resource provided to source cell 1 by candidate cell 2 and the first resource provided to source cell 1 by candidate cell 3. Example 2 of the contents of the first resources configured for the first and second terminal devices is the first resource provided to the first network device by candidate cell 2 and the first resource provided to the first network device by candidate cell 3. The first and second terminal devices are considered to be able to perform subsequent cell switching. For example, after switching from source cell 1 to candidate cell 2, the first and second terminal devices can then continue to switch from candidate cell 2 to candidate cell 3. Therefore, the first resources provided to the first and second terminal devices may further include the first resources provided to other candidates by any candidate cell, for example, the first resources provided to candidate cell 3 by candidate cell 2, and the first resources provided to candidate cell 2 by candidate cell 3. In this way, when subsequent cell switching is performed, the first resources do not need to be reconfigured for the first and second terminal devices. It will be understood that the first network device, the second network device, and the third network device must implement S501 in order to configure the first resources provided to other candidate cells by any candidate cell for the first and second terminal devices.

[0144] S402: The second network device sends the first message to the first network device, and the first network device receives the first message.

[0145] In this embodiment of the present application, a second network device can send a first message to a first network device, and in response, the first network device can receive a first message from the second network device. The first message may indicate a first TA, or the first message may indicate a second TA.

[0146] If the first and second network devices use a CU-DU partitioning architecture, it will be understood that the second network device can send a first message to the first network device via the third network device, and correspondingly, the first network device can receive a first message from the second network device via the third network device. If the first and second network devices do not use a CU-DU partitioning architecture, the second network device can send a first message directly to the first network device, and correspondingly, the first network device can receive a first message directly from the second network device.

[0147] When the first message indicates the first TA, in one implementation, the first message may include first information. The first information indicates that the first TA corresponds to the first terminal device. The first information may include identification information for the first random access preamble and information regarding the first time-frequency position. For example, the first message may indicate TA1, and the first information in the first message may include the random access preamble 1, the random access channel occasion 1, the temporary identifier 1 for the random access radio network, and the system frame number 1.

[0148] In another implementation, the first information may further include second identification information, which identifies the first source cell or first network device.

[0149] For example, if the first source cell and the second source cell are different cells, for instance, if the first source cell is cell 1 and the second source cell is cell 2, then the first information in the first message may include the identification information of cell 1. As a result, the first network device can determine, based on the identification information of cell 1, that the first TA corresponds to the first terminal device.

[0150] In yet another implementation, the first information may further include first identification information, which indicates a first target cell or a second network device. When the first and second network devices use a CU-DU partitioning architecture, in other words, when the first and second network devices are DUs and the third network device is a CU, it will be understood that the first identification information may be assigned by the third network device and notified to the second network device, or assigned by the second network device and notified to the third network device.

[0151] For example, if the first target cell and the second target cell are different cells, as shown in Figure 3f, the source cells of both UE1 and UE2 are cell 1, the target cell of UE1 is cell 2, and the target cell of UE2 is cell 3. UE1 and UE2 send two random access preambles to DU2, to which cells 2 and 3 belong. DU2 then obtains the TA of cell 2 and the TA of cell 3, which are TA1 and TA2, respectively, through calculations based on the two random access preambles. In this case, DU2 can send a first message to DU1. When the first message indicates TA1, the first information in the first message may include the identifier cell2 of cell 2, and as a result, DU1 can determine that TA1 corresponds to UE1.

[0152] In yet another implementation, the first information may further include identification information for the first terminal device. Alternatively, the first information may include only the identification information for the first terminal device, without including the identification information for the first random access preamble, the information for the first time-frequency position, the first identification information, or the second identification information.

[0153] See, for example, Figure 6. After sending a first random access preamble to a second network device, the first terminal device may further transmit its identification information to the second network device via PUSCH, and in response, the second network device may further receive the identification information of the first terminal device from the first terminal device. As a result, the first information in the first message sent to the first network device by the second network device may include the identification information of the first terminal device. Furthermore, the first network device may determine that the first TA corresponds to the first terminal device based on the identification information of the first terminal device. For example, the identification information of the first terminal device may be carried by physical layer signaling (e.g., PUSCH signaling) or by MAC CE messages or RRC layer messages. This is not limited to this embodiment of the present application.

[0154] It will be understood that, after receiving a first random access preamble from a first terminal device, the second network device may determine the identification information of the first random access preamble, information about the first time-frequency location from which the first terminal device transmits the first random access preamble, the second identification information, the first identification information, or the identification information of the first terminal device. In other words, after receiving a first random access preamble from a first terminal device, the first network device may determine the first information.

[0155] Similarly, when the first message indicates the second TA, in one implementation, the first message may include first information. The first information indicates that the second TA corresponds to the second terminal device. The first information may include identification information for the second random access preamble and information regarding the second time-frequency position. For example, the first message indicates TA2, and the first information in the first message may include the random access preamble 2, the random access channel occasion 2, the temporary identifier 2 for the random access radio network, and the system frame number 2.

[0156] In another implementation, the first information may further include a fourth piece of identification information, which indicates a second source cell or a first network device.

[0157] For example, if the first source cell and the second source cell are different cells, for instance, if the first source cell is cell 1 and the second source cell is cell 2, the first information in the first message may include the identification information of cell 2. As a result, the first network device can determine, based on the identification information of cell 2, that the second TA corresponds to the second terminal device.

[0158] In yet another implementation, the first information may further include a third identification information, which indicates a second target cell or a second network device. When the first and second network devices use a CU-DU partitioning architecture, in other words, when the first and second network devices are DUs and the third network device is a CU, it will be understood that the third identification information may be assigned by the third network device and notified to the second network device, or assigned by the second network device and notified to the third network device.

[0159] For example, if the first target cell and the second target cell are different cells, as shown in Figure 3f, the source cells of both UE1 and UE2 are cell 1, the target cell of UE1 is cell 2, and the target cell of UE2 is cell 3. UE1 and UE2 send two random access preambles to DU2, to which cells 2 and 3 belong. DU2, through calculations based on the two random access preambles, obtains the TA of cell 2 and the TA of cell 3, which are TA1 and TA2, respectively. In this case, DU2 can send a first message to DU1. When the first message indicates TA2, the first information in the first message may include the identifier cell3 of cell 3, and as a result, DU1 can determine that TA2 corresponds to UE2.

[0160] In yet another implementation, the first information may further include identification information for a second terminal device. Alternatively, the first information may include only the identification information for a second terminal device, without including identification information for a second random access preamble, information for a second time-frequency position, a third identification information, or a fourth identification information.

[0161] See, for example, Figure 6. After transmitting a second random access preamble to a second network device, the second terminal device may further transmit its identification information to the second network device via PUSCH, and in response, the second network device may further receive its identification information from the second terminal device, and as a result, the first information in the first message transmitted by the second network device to the first network device may include the identification information of the second terminal device. Furthermore, the first network device may determine that the second TA corresponds to the second terminal device based on the identification information of the second terminal device. For example, the identification information of the second terminal device may be carried by physical layer signaling (e.g., PUSCH signaling) or by MAC CE messages or RRC layer messages. This is not limited to this embodiment of the present application.

[0162] In yet another implementation, in S503, after determining the second resource configured for the first terminal device from the first resource, the first network device may send a message to the second network device indicating information about the second resource. Optionally, the first network device may further send a message to the second network device indicating the identification information of the first terminal device. The message may be forwarded by a third network device. After the second network device receives the message indicating information about the second resource, it receives a random access preamble at the corresponding resource location. The second network device receives the random access preamble and, after obtaining a TA by computation, sends the TA to the first network device, which may be forwarded by the third network device. Optionally, when sending the TA, the second network device may further send the identification information of the first terminal device, so that the first network device can determine that the received TA corresponds to the first terminal device.

[0163] In yet another implementation, in S503, the first network device may include identification information for the first target cell in the information relating to the second resource, as indicated in the first synchronization instruction message, and the first target cell is one of at least one candidate cell configured for the first terminal device. For example, eight candidate cells are configured for the first terminal device, and the identifiers of the eight candidate cells are A, B, C, D, E, F, G, and H, respectively, and the identifiers are recorded as cell identifiers on the terminal device side. In this case, the information relating to the second resource, as indicated in the first synchronization instruction message, may include one of the identifiers A to H. However, the first identification information indicated in the first information of S402 may be different from the identification information for the first target cell. For example, the identification information for the first target cell, as indicated by the first identification information, may be the physical cell identifier (PCI) or cell global identifier (CGI) of the first target cell, or another identifier that can indicate the first target cell. The identifier is recorded as the cell identifier on the network device side.

[0164] The first network device can further learn the cell identifier on the terminal device side, the cell identifier on the network device side, and the correspondence between the cell identifier on the terminal device side and the cell identifier on the network device side. The aforementioned information may be generated by the first network device. For example, the third network device notifies the first network device of the cell identifier on the network device side, and the first network device generates the correspondence between the cell identifier on the terminal device side and the cell identifier on the network device side. Alternatively, the aforementioned information may be generated by the third network device. For example, the third network device notifies the first network device of the cell identifier on the terminal device side, the cell identifier on the network device side, and the correspondence between the cell identifier on the terminal device side and the cell identifier on the network device side. For example, the notification process is completed in S502.

[0165] S403: The first network device transmits the first TA to the first terminal device based on the first information, or the first network device transmits the second TA to the second terminal device based on the first information.

[0166] In this embodiment of the present application, when the first message indicates the first TA, in S503, the first network device determines from the first resources which second resources are to be provided to the first terminal device and indicates information about the second resources in the first synchronization instruction message sent to the first terminal device, so that the first terminal device uses the second resources to perform uplink synchronization with the second network device. Thus, the first network device can determine whether the first information contained in the first message matches the information about the second resource, and if the first information contained in the first message matches the information about the second resource, the first network device determines that the first TA corresponds to the first terminal device and transmits the first TA to the first terminal device.

[0167] For example, the first TA may be carried by a switch command or a downlink message. A switch command may indicate that the first terminal device has configured a cell managed by the second network device as a candidate cell. The downlink message may be a random access response message or a MAC CE message. This is not limited to this embodiment of the present application.

[0168] Optionally, a switch command or downlink message may further include an uplink grant for the first source cell, so that after receiving the first TA, the first terminal device can use the uplink grant for the first source cell to send an uplink message to the first network device. The uplink message indicates that the first terminal device has successfully received the first TA, in other words, that the first terminal device has successfully completed uplink synchronization with the second network device.

[0169] Similarly, when the first message indicates the second TA, the first network device can determine whether the first information contained in the first message matches information about resources provided to the second terminal device. If the first information contained in the first message matches information about resources provided to the second terminal device, the first network device determines that the second TA corresponds to the second terminal device and sends the second TA to the second terminal device.

[0170] Optionally, after the first or second terminal device has completed one cell switching, the first or second terminal device can perform subsequent cell switching. Since the first network device knows the first TA of the first target cell corresponding to the first terminal device or the second TA of the second target cell corresponding to the second terminal device, after the first or second terminal device switches from the first network device to the second network device, the first network device can send a message to the second network device indicating the identification information of the first terminal device, the first identification information and the first TA, or a message indicating the identification information of the second terminal device, the third identification information and the second TA, so that the second network device learns the TA of the first target cell corresponding to the first terminal device or the TA of the second target cell corresponding to the second terminal device, and helps the first or second terminal device to continue switching without random access. It will be understood that a message sent from the first network device to the second network device can be forwarded using the third network device.

[0171] In one implementation, the first network device can indicate a Terminal Aid (TA) to a terminal device (e.g., the first or second terminal device) in a switch command (e.g., step 6 in Figure 3b). If the first network device successfully obtains the TA of the terminal device to be switched, the first network device can explicitly include the TA in the switch command, and the terminal device uses the TA to perform cell switching without random access. If the first network device does not obtain the TA of the terminal device to be switched, the first network device can indicate a special value in the TA field of the switch command, which can indicate that the TA was not obtained, that the TA is invalid, or that the terminal device to be switched should perform switching without random access. When the TA field has m binary bits, the first network device can set all m binary bits to 1 to indicate that the TA field has a special value, further indicating that the TA was not obtained, that the TA is invalid, or that the terminal device should perform random access-based switching. When m is equal to 12, the first network device can set the TA field as a special value of 111111111111 (i.e., 4095 in decimal notation). It will be understood that the special value must be set to an invalid TA value. If a valid TA value is in the interval a to b, a value not in the interval a to b can be set to a special value, for example, b+1. The specific value is not limited to this embodiment of the present application. According to this solution, the format design of the switch command may be applied to switching scenarios without random access and switching scenarios based on random access, and the terminal device can quickly obtain the content indicated by the switch command through parsing.

[0172] In another implementation, the first network device indicates the TA to the terminal device in a downlink message before the switch command (for example, step 5b in Figure 3c). Since the terminal device to be switched can send random access preambles to multiple candidate cells in a short period of time in order to obtain the TA in advance, the downlink message in step 5b can carry identification information indicating the TA and the corresponding candidate cell.

[0173] In yet another implementation, the first network device can further indicate the beam direction of the target cell in a switch command. For example, the transmission configuration indicator (TCI) state indicates the beam direction that needs to be used by the terminal device. In a switching process without random access, the terminal device sends an uplink message to the target cell using the indicated beam direction and TA. There are two types of TCI states: Joint TCI State and Separate TCI State. Joint TCI State indicates uplink (UL) and downlink (DL) beam directions, Separate UL TCI State indicates uplink beam direction, and Separate DL TCI State indicates downlink beam direction. When the first network device needs to indicate the beam direction that needs to be used by the terminal device in the target cell in a switch command, the first network device needs to know the type of TCI State configured by the second network device for the terminal device. Therefore, in step 1 of Figure 3a, Figure 3b, or Figure 3c, the candidate DU (or target DU) informs the source DU of the type of TCI State configured for the candidate cell (or target cell), for example, whether the type is Joint or Separate.

[0174] Solution 2 Figure 7 is a schematic flowchart of another timing advance acquisition method according to one embodiment of the present application. The method can be applied to the communication system shown in Figure 1, but is not limited thereto. The method can be applied to Scenario 2, but is not limited thereto. In Scenario 2, the first target cell and the second target cell may be the same cell or different cells. This is not limited to this embodiment of the present application. The method includes the following steps.

[0175] S701: The first terminal device transmits a first random access preamble to the second network device, and in response, the second network device receives the first random access preamble from the first terminal device. The second terminal device transmits a second random access preamble to the second network device, and in response, the second network device receives the second random access preamble from the second terminal device.

[0176] In this embodiment of the present application, a first terminal device can transmit a first random access preamble to a second network device, and in response, the second network device can receive the first random access preamble from the first terminal device. Similarly, a second terminal device can transmit a second random access preamble to a second network device, and in response, the second network device can receive the second random access preamble from the second terminal device. It will be understood that the first random access preamble and the second random access preamble may be the same random access preamble or different random access preambles. This is not limited to this embodiment of the present application.

[0177] The second network device can further obtain the first TA from the first terminal device by calculation based on the first random access preamble, and can obtain the second TA from the second terminal device by calculation based on the second random access preamble.

[0178] For example, if the first target cell and the second target cell are the same cell, then as shown in Figure 3e, the source cell for UE1 is cell 1 and the source cell for UE2 is cell 2. The target cell for both UE1 and UE2 is cell 3. The DU to which cell 1 belongs is DU1, in other words, the source DU for UE1 is DU1. The DU to which cell 2 belongs is DU2, in other words, the source DU for UE2 is DU2. The DU to which cell 3 belongs is DU3, in other words, the target DU for both UE1 and UE2 is DU3. UE1 and UE2 send two random access preambles to DU2. DU3 obtains two different TAs for cell 3, which are TA1 and TA2, respectively, through calculations based on the two random access preambles.

[0179] Based on the implementation process in Figure 7, the steps shown in Figure 8 may be further performed in this application.

[0180] In S801, the third network device can send a second request message (or a seventh message) to the second network device, and in response, the second network device can receive the second request message from the third network device.

[0181] A second request message may be used to request a fourth resource in at least one candidate cell. The fourth resource may be used by terminal devices in the first source cell (e.g., the first terminal device) and terminal devices in the second source cell (e.g., the second terminal device) to perform uplink synchronization with a second network device. Optionally, the fourth resource may also be used by terminal devices served by the first network device (e.g., the first terminal device) and terminal devices served by the fourth network device (e.g., the second network device) to perform uplink synchronization with the second network device.

[0182] For example, information about the fourth resource may include one or more of the following: identification information for the random access preamble transmitted by terminal devices in the first and second source cells when a terminal device performs uplink synchronization with the second network device; time-frequency location information for the random access preamble transmitted by terminal devices in the first and second source cells when a terminal device performs uplink synchronization with the second network device; and beam direction information corresponding to the time-frequency location information for the random access preamble transmitted by terminal devices in the first and second source cells when a terminal device performs uplink synchronization with the second network device. It will be understood that information about the fourth resource at the granularity of the first and second source cells may alternatively be at the granularity of the first and fourth network devices. Specifically, the information relating to the fourth resource may include one or more of the following information: identification information for a random access preamble transmitted by a terminal device served by the first and fourth network devices when the terminal device performs uplink synchronization with the second network device; time-frequency location information for the random access preamble transmitted by the terminal device served by the first and fourth network devices when the terminal device performs uplink synchronization with the second network device; and beam direction information corresponding to the time-frequency location information for the random access preamble transmitted by the terminal device served by the first and fourth network devices when the terminal device performs uplink synchronization with the second network device.In this embodiment of the present application, a candidate network device (or referred to as a target network device) (e.g., a second network device) can allocate a fourth resource to multiple source cells (e.g., a first source cell and a second source cell), or to multiple source network devices (e.g., a first network device and a fourth network device). One allocated fourth resource may be provided by each candidate cell.

[0183] In one implementation, the second request message may include information about the amount of the requested fourth resource. The number of the requested fourth resource may be obtained by the third network device based on the number of terminal devices in the first and second source cells, or based on the number of terminal devices in the first and second source cells that are configured as candidate cells and managed by the second network device. For example, if the first source cell is cell 1, the second source cell is cell 2, the cell managed by the second network device is cell 3, and the terminal devices in cell 1 and cell 2 include terminal device 1, terminal device 2, and terminal device 3, and the terminal devices in cell 1 and cell 2 that access cell 3 include terminal device 1 and terminal device 2, then the third network device can obtain the amount of resources used by the terminal devices in cell 1 and cell 2, or by terminal devices in cell 1 and cell 2 that are configured to perform uplink synchronization with the second network device with cell 3 as a candidate cell, based on the number of terminal devices in cell 1 and cell 2, or based on the number of terminal devices in cell 1 and cell 2 that are configured with cell 3 as a candidate cell, and can indicate in a second request message sent to the second network device the amount of resources used by the terminal devices in cell 1 and cell 2, or by terminal devices in cell 1 and cell 2 that are configured with cell 3 as a candidate cell for performing uplink synchronization with the second network device. For example, the number can be large, medium, or small.

[0184] In another implementation, the second request message may further include one or more of the following information: a first identification information indicating a first target cell, a second identification information indicating a first source cell, a third identification information indicating a second target cell, and a fourth identification information indicating a second source cell. For example, if the first source cell is cell 1, the second source cell is cell 2, and the first and second target cells are cell 3, the third network device may indicate the identification information for cell 1, the identification information for cell 2, and / or the identification information for cell 3 in the second request message sent to the second network device, and the second network device may determine, based on the identification information for cell 1, the identification information for cell 2, and the identification information for cell 3, that the second request message is used to request that the resources of cell 3 be allocated to the terminal devices in cell 1 and cell 2 so that the terminal devices in cell 1 and cell 2 can perform uplink synchronization with cell 3. It will be understood that the first identification information can alternatively indicate the second network device to which the first target cell belongs, the second identification information can alternatively indicate the first network device to which the first source cell belongs, the third identification information can alternatively indicate the second network device to which the second target cell belongs, and the fourth identification information can alternatively indicate the fourth network device to which the second source cell belongs.

[0185] It will be understood that the first, second, third, and / or fourth identification information may be explicitly or implicitly indicated in the second request message. This is not limited to this embodiment of the present application. When the first, second, third, and / or fourth identification information is implicitly indicated, there is a correspondence between the cell identifier and the F1 interface identifier between the CU and DU. The CU and DU can determine the corresponding cell identifier based on the F1 interface identifier.

[0186] In yet another implementation, the second request message may be a request message at the terminal device level. For example, the second request message may further include one or more of the following information: identification information for the first terminal device, identification information for the second terminal device, instruction information for requesting a fourth resource shared by the first and second terminal devices, instruction information for requesting a fourth resource dedicated to the first terminal device, and instruction information for requesting a fourth resource dedicated to the second terminal device. In this way, if the first terminal device requires low latency, the second network device can allocate a fourth resource dedicated to the first terminal device. Thus, in the subsequent S804, the first network device can quickly select a second resource to be used by the first terminal device to perform early synchronization based on the first resource determined by the fourth resource, and as a result, the first terminal device can quickly complete early TA acquisition and perform switching without random access in order to meet the low latency requirement.

[0187] In S802, the second network device can send a second response message (or a sixth message) to the third network device, and in response, the third network device can receive a second response message from the second network device.

[0188] The second response message may indicate a fourth resource.

[0189] In one implementation, the fourth resource may be different from the third resource of at least one candidate cell, and the third resource is used by a terminal device in at least one candidate cell to perform uplink synchronization with the second network device. For example, if the first source cell is cell 1, the second source cell is cell 2, and at least one candidate cell is cell 3, when the second network device assigns the resources of cell 3 to terminal devices in cells 1 and 2 so that the terminal devices in cells 1 and 2 can perform uplink synchronization with cell 3, the resources assigned to the terminal devices in cells 1 and 2 are different from the resources assigned to the terminal devices in cell 3, so when the terminal devices in cells 1 and 2 perform uplink synchronization with cell 3, the terminal devices in cell 3's access to cell 3 is not affected.

[0190] It will be understood that the fourth and third resources may be random access preambles having different route sequences. For example, in 64 random access preambles, preambles a1, ..., and a64 may be assigned to terminal devices in cells 1 and 2, and in 64 other random access preambles, preambles b1, ..., and b64 may be assigned to terminal devices in cell 3. Alternatively, the fourth and third resources may have different time-frequency positions for transmitting random access preambles. For example, the time-frequency position for transmitting random access preambles assigned to terminal devices in cells 1 and 2 is time-frequency position 1, and the time-frequency position for transmitting random access preambles assigned to terminal devices in cell 3 is time-frequency position 2. This is not limited to this embodiment of the present application.

[0191] In S803, the third network device can determine the first and fifth resources from the fourth resource, send a third response message (or eighth message) to the first network device, and send a fourth response message to the fourth network device. In response, the first network device can receive the third response message from the third network device, and the fourth network device can receive the fourth response message from the third network device.

[0192] The first resource may be used by a terminal device in the first source cell to perform uplink synchronization with the second network device. The fifth resource may be used by a terminal device in the second source cell to perform uplink synchronization with the second network device. The third response message may indicate the first resource. The fourth response message may indicate the fifth resource. Optionally, the first resource may be used by a terminal device served by the first network device (e.g., the first terminal device) to perform uplink synchronization with the second network device. Alternatively, the fifth resource may be used by a terminal device served by the fourth network device (e.g., the second terminal device) to perform uplink synchronization with the second network device.

[0193] For example, information about the first resource may include one or more of the following: identification information for a random access preamble transmitted by the terminal device in the first source cell when the terminal device performs uplink synchronization with the second network device (e.g., identification information for the first random access preamble); information about the time-frequency position to which the terminal device in the first source cell transmits the random access preamble when the terminal device performs uplink synchronization with the second network device (e.g., information about the first time-frequency position); and information about the beam direction corresponding to the information about the time-frequency position to which the terminal device in the first source cell transmits the random access preamble when the terminal device performs uplink synchronization with the second network device (e.g., information about the first beam direction, which is used by the first terminal device to determine the first time-frequency position). It will be understood that the information about the first resource at the granularity of the first source cell may, alternatively, be at the granularity of the first network device. Specifically, the information relating to the first resource may include one or more of the following information: identification information for a random access preamble transmitted by a terminal device served by the first network device when the terminal device performs uplink synchronization with the second network device; time-frequency location information for the random access preamble transmitted by the terminal device served by the first network device when the terminal device performs uplink synchronization with the second network device; and beam direction information corresponding to the time-frequency location information for the random access preamble transmitted by the terminal device served by the first network device when the terminal device performs uplink synchronization with the second network device.

[0194] For example, the information relating to the first time-frequency position may include one or more of the following information: identification information for a random access channel occasion, information relating to a temporary identifier for a random access radio network, or system frame number indicating a value of at least one bit of the system frame number.

[0195] For example, information about the fifth resource may include one or more of the following: identification information for a random access preamble transmitted by the terminal device in the second source cell when the terminal device performs uplink synchronization with the second network device (e.g., identification information for the second random access preamble); information about the time-frequency position to which the terminal device in the second source cell transmits the random access preamble when the terminal device performs uplink synchronization with the second network device (e.g., information about the second time-frequency position); and beam direction information corresponding to the time-frequency position to which the terminal device in the first source cell transmits the random access preamble when the terminal device performs uplink synchronization with the second network device (e.g., information about the second beam direction, which is used by the second terminal device to determine the second time-frequency position). It will be understood that the information about the fifth resource at the granularity of the second source cell may alternatively be at the granularity of the fourth network device. Specifically, the information relating to the fifth resource may include one or more of the following: identification information for a random access preamble transmitted by a terminal device serviced by the fourth network device when the terminal device performs uplink synchronization with the second network device; time-frequency location information for the random access preamble transmitted by the terminal device serviced by the fourth network device when the terminal device performs uplink synchronization with the second network device; and beam direction information corresponding to the time-frequency location information for the random access preamble transmitted by the terminal device serviced by the fourth network device when the terminal device performs uplink synchronization with the second network device.

[0196] In one implementation, the first resource may be different from the fifth resource. The first and fifth resources may be random access preambles having different route sequences, or the first and fifth resources may have different time-frequency positions for transmitting the random access preamble. This is not limited to this embodiment of the present application.

[0197] In one implementation configuration, the third network device can obtain the number of first resources based on the number of terminal devices in the first source cell or the number of terminal devices in the first source cell that are configured with cells managed by the second network device as candidate cells, and obtain the number of fifth resources based on the number of terminal devices in the second source cell or the number of terminal devices in the second source cell that are configured with cells managed by the second network device as candidate cells.

[0198] It will be understood that the third network device can divide the fourth resource into a first resource and a fifth resource at the cell granularity, or into a first resource and a fifth resource at the bandwidth part (BWP) granularity. For example, the first resource may be a resource corresponding to a first BWP of at least one candidate cell, and the fifth resource may be a resource corresponding to a second BWP of at least one candidate cell. This is not limited to this embodiment of the present application.

[0199] In S804, the first network device can determine the second resource from the first resource and send a first synchronization instruction message to the first terminal device, to which the first terminal device can receive the first synchronization instruction message from the first network device; the fourth network device can determine the sixth resource from the fifth resource and send a second synchronization instruction message to the second terminal device, to which the second terminal device can receive the second synchronization instruction message from the fourth network device.

[0200] For further explanation regarding the statement in S804, "The first network device determines the second resource from the first resource and sends a first synchronization instruction message to the first terminal device. In response, the first terminal device receives the first synchronization instruction message from the first network device. The fourth network device sends a second synchronization instruction message to the second terminal device. In response, the second terminal device can receive the second synchronization instruction message from the fourth network device," please refer to the explanation in S503. Details will not be repeated here.

[0201] The sixth resource may be used by the second terminal device to perform uplink synchronization with the second network device.

[0202] For example, the information regarding the sixth resource may include one or more of the following: identification information for a random access preamble transmitted by the second terminal device when the second terminal device performs uplink synchronization with the second network device (e.g., identification information for the second random access preamble); information regarding the time-frequency position to which the second terminal device transmits the random access preamble when the second terminal device performs uplink synchronization with the second network device (e.g., information regarding the second time-frequency position); and beam direction information corresponding to the time-frequency position information to which the first terminal device transmits the random access preamble when the first terminal device performs uplink synchronization with the second network device (e.g., information regarding the second beam direction, which is used by the second terminal device to determine the second time-frequency position). In other words, the second instruction information may include information regarding the sixth resource.

[0203] Optionally, in S802, S803, and S804, the fourth resources configured for the first and second terminal devices may first be transmitted to the third network device by the second network device, then the third network device determines the first resource from the first resources and transmits the first resource to the first network device, determines the fifth resource from the first resources and transmits the fifth resource to the fourth network device, then the first network device determines the second resource from the first resources and transmits the second resource to the first terminal device, and the fourth network device determines the sixth resource from the fifth resource and transmits the sixth resource to the second terminal device. Example 1 of the fourth resources configured for the first and second terminal devices is the fourth resource provided by candidate cell 2 to source cell 1 and source cell 2, and the fourth resource provided by candidate cell 3 to source cell 1 and source cell 2. Example 2 of the contents of the fourth resource configured for the first and second terminal devices is the fourth resource provided by candidate cell 2 to the first and fourth network devices, and the fourth resource provided by candidate cell 3 to the first and fourth network devices. The first and second terminal devices are considered to be able to perform subsequent cell switching. For example, after switching from source cell 1 to candidate cell 2, and from source cell 2 to candidate cell 2, the first and second terminal devices can switch from candidate cell 2 to candidate cell 3, and then continue to switch from candidate cell 2 to candidate cell 4. Thus, the fourth resource provided to the first and second terminal devices may further include the fourth resource provided by any candidate cell to another candidate cell, for example, the fourth resource provided by candidate cell 2 to candidate cell 3 and candidate cell 4.In this way, when subsequent cell switching is performed, the fourth resource does not need to be reconfigured for the first and second terminal devices. It will be understood that in order to configure the fourth resource provided by any candidate cell for another candidate cell for the first and second terminal devices, the second and third network devices must implement S801.

[0204] Based on the implementation process in Figure 7, the steps shown in Figure 9 may be further performed in this application.

[0205] In S901, the third network device can send a second request message to the second network device, and in response, the second network device can receive a second request message from the third network device.

[0206] For details on S901, please refer to the explanation for S801. We will not repeat the details here.

[0207] In S902, the second network device can determine the first and fifth resources from the fourth resource and send a second response message to the third network device, to which the third network device receives a second response message from the second network device.

[0208] For further explanation regarding S902, "The second network device determines the first and fifth resources from the fourth resource," please refer to the explanation in S803. For further explanation regarding S902, "The second network device sends a second response message to the third network device, and in response, the third network device receives a second response message from the second network device," please refer to the explanation in S802. Details will not be repeated here.

[0209] In S903, the third network device can send a third response message to the first network device and a fourth response message to the fourth network device. In response, the first network device can receive a third response message from the third network device, and the fourth network device can receive a fourth response message from the third network device.

[0210] For S903, please refer to the explanation for S803. We will not repeat the details here.

[0211] In S904, the first network device can determine the second resource from the first resource and send a first synchronization instruction message to the first terminal device, to which the first terminal device can receive the first synchronization instruction message from the first network device; the fourth network device can determine the sixth resource from the fifth resource and send a second synchronization instruction message to the second terminal device, to which the second terminal device can receive the second synchronization instruction message from the fourth network device.

[0212] For S904, please refer to the explanation for S804. We will not repeat the details here.

[0213] S702: The second network device sends the fifth message to the third network device, and in response, the third network device receives the fifth message from the second network device.

[0214] In this embodiment of the present application, a second network device can send a fifth message to a third network device, and in response, the third network device can receive a fifth message from the second network device. The fifth message may indicate a first TA, or the fifth message may indicate a second TA.

[0215] When the fifth message indicates the first TA, in one implementation, the fifth message may include second information. The second information indicates that the first TA corresponds to a first network device to which the first source cell of the first terminal device belongs. The second information may include one or more of the following: identification information and information regarding the first time-frequency position of the first random access preamble, and second identification information indicating the first source cell or the first network device. For example, if the fifth message indicates TA1, the second information in the fifth message may include random access preamble 1, random access channel occasion 1, temporary identifier 1 of the random access radio network, system frame number 1, and cell 1.

[0216] It will be understood that the second identification information is obtained by the second network device based on the first random access preamble and the first resource. For example, after receiving the first random access preamble from the first terminal device, the second network device can determine whether the identification information of the first random access preamble is present in the information about the first resource. If the identification information of the first random access preamble is present in the information about the first resource, then the first resource is a resource used by a terminal device in the first source cell, or a resource served by the first network device to perform uplink synchronization with the second network device. Therefore, it can be determined that the network device to which the source cell of the terminal device corresponding to the first TA obtained by calculation based on the first random access preamble belongs is the network device to which the first source cell belongs, i.e., the first TA corresponds to the first network device. Therefore, the second network device can include the second identification information in the second information of the fifth message sent to the third network device, and as a result, the third network device can determine, based on the second identification information, that the first TA corresponds to the first network device and send the fifth message to the first network device.

[0217] In another implementation, the third network device can divide the fourth resource into a first resource and a fifth resource at the cell granularity, in other words, the first resource may be a resource corresponding to the first BWP of at least one candidate cell, the fifth resource may be a resource corresponding to the second BWP of at least one candidate cell, and the second information may further include identification information of the first BWP.

[0218] Similarly, when the fifth message indicates the second TA, in one implementation, the fifth message may include second information. The second information indicates that the second TA corresponds to a fourth network device to which the second source cell of the second terminal device belongs. The second information may include one or more of the following: identification information and information regarding the second time-frequency position of the second random access preamble, and fourth identification information indicating the second source cell or the fourth network device. For example, if the fifth message indicates TA2, the second information in the fifth message may include the random access preamble 2, the random access channel occasion 2, the temporary identifier of the random access radio network 2, the system frame number 2, and the cell 2.

[0219] It will be understood that the fourth identification information is obtained by the second network device based on the second random access preamble and the fifth resource. For example, after receiving the second random access preamble from the second terminal device, the second network device can determine whether the identification information of the second random access preamble exists in the fifth resource. If the identification information of the second random access preamble exists in the information about the fifth resource, then it can be determined that the network device to which the source cell of the terminal device corresponding to the second TA, obtained by calculation based on the second random access preamble, belongs is the network device to which the second source cell belongs, i.e., the second TA corresponds to the fourth network device. Therefore, the second network device can include the fourth identification information in the second information of the fifth message sent to the third network device, and as a result, the third network device can determine, based on the fourth identification information, that the second TA corresponds to the fourth network device and send the fifth message to the fourth network device.

[0220] S703: The third network device sends a fifth message to the first or fourth network device based on the second information, and in response, the first or fourth network device receives the fifth message from the third network device.

[0221] In this embodiment of the present application, when the fifth message indicates a first TA, if the second information includes identification information for a first random access preamble and information regarding a first time-frequency position, the third network device can determine whether the identification information for a first random access preamble and information regarding a first time-frequency position are present in the information regarding a first resource. If the identification information for a first random access preamble and information regarding a first time-frequency position are present in the information regarding a first resource, the first resource is a resource used by terminal devices in a first source cell to perform uplink synchronization with a second network device. Therefore, based on the identification information for a first random access preamble and information regarding a first time-frequency position, the third network device can determine that the first TA indicated by the fifth message corresponds to the first network device to which the first source cell belongs, and can send the fifth message to the first network device.

[0222] If the second information includes the second identification information, the third network device may determine, based on the second identification information, that the first TA indicated by the fifth message corresponds to the first network device to which the first source cell belongs, and may send the fifth message to the first network device.

[0223] Similarly, when the fifth message indicates the second TA, if the second information includes the identification information of the second random access preamble and information regarding the second time-frequency position, the third network device can determine whether the identification information of the second random access preamble and information regarding the second time-frequency position are present in the information regarding the fifth resource. If the information regarding the fifth resource includes the identification information of the second random access preamble and information regarding the second time-frequency position, the fifth resource is a resource used by terminal devices in the second source cell to perform uplink synchronization with the second network device. Therefore, based on the identification information of the second random access preamble and information regarding the second time-frequency position, the third network device can determine that the second TA indicated by the fifth message corresponds to the fourth network device to which the second source cell belongs, and can send the fifth message to the fourth network device.

[0224] If the second information includes the fourth identification information, the third network device may determine, based on the fourth identification information, that the second TA indicated by the fifth message corresponds to the fourth network device to which the second source cell belongs, and may send the fifth message to the fourth network device.

[0225] Solution 3 Figure 10 is a schematic flowchart of yet another timing advance acquisition method according to one embodiment of the present application. The method can be applied to the communication system shown in Figure 1, but is not limited thereto. The method can be applied to Scenario 3, but is not limited thereto. In Scenario 3, the first source cell and the third source cell may be the same cell or different cells, and the first target cell, the second target cell, and the third target cell may be the same cell or different cells. This is not limited to this embodiment of the present application. For ease of explanation, this embodiment of the present application uses an example in which the second source cell and the third source cell are the same cell. Hereinafter, the second source cell and the third source cell will be collectively referred to as the second source cell. The method includes the following steps.

[0226] S1001: The first terminal device transmits a first random access preamble to the second network device, and in response, the second network device receives the first random access preamble from the first terminal device. The second terminal device transmits a second random access preamble to the second network device, and in response, the second network device receives the second random access preamble from the second terminal device. The third terminal device transmits a third random access preamble to the second network device, and in response, the second network device receives the third random access preamble from the third terminal device.

[0227] In this embodiment of the present application, a first terminal device can transmit a first random access preamble to a second network device, and in response, the second network device can receive the first random access preamble from the first terminal device. Similarly, a second terminal device can transmit a second random access preamble to a second network device, and in response, the second network device can receive the second random access preamble from the second terminal device. A third terminal device can also transmit a third random access preamble to the second network device, and in response, the second network device can receive the third random access preamble from the third terminal device. It will be understood that the first random access preamble, the second random access preamble, and the third random access preamble may be the same random access preamble or different random access preambles. This is not limited to this embodiment of the present application.

[0228] The second network device can further obtain a first TA by calculation based on a first random access preamble from the first terminal device, obtain a second TA by calculation based on a second random access preamble from the second terminal device, and obtain a third TA by calculation based on a third random access preamble from the third terminal device.

[0229] For example, see Figure 3g. The source cell for UE1 is cell 1, and the source cells for UE2 and UE3 are cell 2. The target cell for UE1, UE2, and UE3 is cell 3. The DU to which cell 1 belongs is DU1, in other words, the source DU for UE1 is DU1. The DU to which cell 2 belongs is DU2, in other words, the source DU for UE2 and UE3 is DU2. The DU to which cell 3 belongs is DU3, in other words, the target DU for UE1, UE2, and UE3 is DU3. UE1, UE2, and UE3 send three random access preambles to DU2. The random access preambles sent by UE1 and UE2 are different, while the random access preambles sent by UE2 and UE3 are the same. DU3 obtains three different TAs for cell 3, which are TA1, TA2, and TA3, respectively, through calculations based on the three random access preambles.

[0230] Based on the implementation process in Figure 10, the steps shown in Figure 11 may be further performed in this application.

[0231] In S1101, the third network device can send a second request message to the second network device, and in response, the second network device can receive a second request message from the third network device.

[0232] For S1101, please refer to the explanation for S801. Details will not be repeated here.

[0233] In S1102, the second network device can send a second response message to the third network device, and in response, the third network device can receive a second response message from the second network device.

[0234] For S1102, please refer to the explanation for S802. Details will not be repeated here.

[0235] In S1103, the third network device can determine the first and fifth resources from the fourth resource, send a third response message to the first network device, and send a fourth response message to the fourth network device. In response, the first network device can receive a third response message from the third network device, and the fourth network device can receive a fourth response message from the third network device.

[0236] For S1103, please refer to the explanation for S803. Details will not be repeated here.

[0237] In S1104, the first network device can determine the second resource from the first resource and send a first synchronization instruction message to the first terminal device, to which the first terminal device can receive the first synchronization instruction message from the first network device; the fourth network device can determine the sixth and seventh resources from the fifth resource and send a second synchronization instruction message to the second terminal device and a third synchronization instruction message to the third terminal device, to which the second terminal device can receive the second synchronization instruction message from the fourth network device and the third terminal device can receive the third synchronization instruction message from the fourth network device.

[0238] For further explanation regarding the statement in S1104, "The first network device can determine the second resource from the first resource and send a first synchronization instruction message to the first terminal device, and in response, the first terminal device can receive the first synchronization instruction message from the first network device; the fourth network device can determine the sixth resource from the fifth resource and send a second synchronization instruction message to the second terminal device, and in response, the second terminal device can receive the second synchronization instruction message from the fourth network device," please refer to the explanation in S804. Details will not be repeated here.

[0239] The seventh resource may be used by the third terminal device to perform uplink synchronization with the second network device.

[0240] For example, the information relating to the seventh resource may include one or more of the following: identification information for a random access preamble transmitted by the third terminal device when the third terminal device performs uplink synchronization with the second network device (e.g., identification information for the third random access preamble); information relating to the time-frequency location to which the third terminal device transmits the random access preamble when the third terminal device performs uplink synchronization with the second network device (e.g., information relating to the third time-frequency location); and beam direction information corresponding to the time-frequency location to which the third terminal device transmits the random access preamble when the third terminal device performs uplink synchronization with the second network device (e.g., information relating to the third beam direction, which is used by the third terminal device to determine the third time-frequency location).

[0241] A third synchronization instruction message may instruct a third terminal device to perform uplink synchronization with the second network device.

[0242] For example, the third synchronization instruction message may include one or more of the following information: identification information for the third random access preamble, information regarding the third time-frequency position, and information regarding the third beam direction. In other words, the third synchronization instruction message may include information regarding the seventh resource.

[0243] Based on the implementation process in Figure 10, the steps shown in Figure 12 may be further performed in this application.

[0244] In S1201, the third network device can send a second request message to the second network device, and in response, the second network device can receive a second request message from the third network device.

[0245] For S1201, please refer to the explanation for S801. Details will not be repeated here.

[0246] In S1202, the second network device can determine the first and fifth resources from the fourth resource and send a second response message to the third network device, to which the third network device receives a second response message from the second network device.

[0247] For S1202, please refer to the explanation for S802. Details will not be repeated here.

[0248] In S1203, the third network device can send a third response message to the first network device and a fourth response message to the fourth network device. In response, the first network device can receive a third response message from the third network device, and the fourth network device can receive a fourth response message from the third network device.

[0249] For S1203, please refer to the explanation for S803. Details will not be repeated here.

[0250] In S1204, the first network device can determine the second resource from the first resource and send a first synchronization instruction message to the first terminal device, to which the first terminal device can receive the first synchronization instruction message from the first network device; the fourth network device can determine the sixth and seventh resources from the fifth resource and send a second synchronization instruction message to the second terminal device and a third synchronization instruction message to the third terminal device, to which the second terminal device can receive the second synchronization instruction message from the fourth network device and the third terminal device can receive the third synchronization instruction message from the fourth network device.

[0251] For S1204, please refer to the explanation for S1104. Details will not be repeated here.

[0252] S1002: The second network device sends the ninth message to the third network device, and in response, the third network device receives the ninth message from the second network device.

[0253] The second network device can send the ninth message to the third network device, and in response, the third network device can receive the ninth message from the second network device. The ninth message can indicate the first TA, the ninth message can indicate the second TA, and the ninth message can indicate the third TA.

[0254] When the ninth message indicates the first TA, in one implementation, the ninth message may include third information. The third information may indicate that the first TA corresponds to a first terminal device, or that the first TA corresponds to a first network device to which the first source cell of the first terminal device belongs. The third information may include one or more of the following: identification information for the first random access preamble and information regarding the first time-frequency position. For example, if the ninth message indicates TA1, the third information in the ninth message may include random access preamble 1, random access channel occasion 1, temporary identifier 1 for the random access radio network, and system frame number 1.

[0255] In another implementation, the third piece of information may further include second identification information that identifies a first source cell or a first network device.

[0256] In yet another implementation, the third piece of information may further include first identification information that indicates a first target cell or a second network device.

[0257] In yet another implementation, the third piece of information may further include identification information for the first terminal device.

[0258] In yet another implementation, the third network device can divide the fourth resource into a first resource and a fifth resource at the cell granularity, in other words, the first resource may be the resource corresponding to the first BWP of at least one candidate cell, the fifth resource may be the resource corresponding to the second BWP of at least one candidate cell, and the third information may further include identification information of the first BWP.

[0259] Similarly, when the ninth message indicates the second TA, in one implementation, the ninth message may include third information. The third information may indicate that the second TA corresponds to the second terminal device, or that the second TA corresponds to the fourth network device to which the second source cell of the second terminal device belongs. The third information may include one or more of the following: identification information for the second random access preamble and information regarding the second time-frequency position. For example, if the ninth message indicates TA2, the third information in the ninth message may include the random access preamble 2, the random access channel occasion 2, the temporary identifier 2 for the random access radio network, and the system frame number 2.

[0260] In another implementation, the third piece of information may further include a fourth piece of identification information that identifies a second source cell or a fourth network device.

[0261] In yet another implementation, the third information may further include third identification information that indicates a second target cell or a second network device.

[0262] In yet another implementation, the third piece of information may further include identification information for the second terminal device.

[0263] In yet another implementation, the third network device can divide the fourth resource into a first resource and a fifth resource at the cell granularity, in other words, the first resource may be a resource corresponding to the first BWP of at least one candidate cell, the fifth resource may be a resource corresponding to the second BWP of at least one candidate cell, and the third information may further include identification information of the second BWP.

[0264] If the ninth message indicates a third TA, in one implementation, the ninth message may include third information. The third information may indicate that the third TA corresponds to a third terminal device, or that the third TA corresponds to a fourth network device to which the second source cell of the third terminal device belongs. The third information may include one or more of the following: identification information for a third random access preamble and information regarding a third time-frequency position. For example, if the ninth message indicates TA3, the third information in the ninth message may include a random access preamble 3, a random access channel occasion 3, a temporary identifier for a random access radio network 3, and a system frame number 3.

[0265] In another implementation, the third information may further include a fifth identification information that identifies a third source cell or a fourth network device.

[0266] In yet another implementation, the third information may further include third identification information that indicates a second target cell or a second network device.

[0267] In yet another implementation, the third piece of information may further include identification information for the third terminal device.

[0268] In yet another implementation, the third network device can divide the fourth resource into a first resource and a fifth resource at the cell granularity, in other words, the first resource may be a resource corresponding to the first BWP of at least one candidate cell, the fifth resource may be a resource corresponding to the second BWP of at least one candidate cell, and the third information may further include identification information of the second BWP.

[0269] S1003: The third network device sends the ninth message based on the third information to the first or fourth network device, and in response, the first or fourth network device receives the ninth message from the third network device.

[0270] In this embodiment of the present application, when the ninth message indicates a first TA, if the third information includes identification information for a first random access preamble and information regarding a first time-frequency position, or if the third information includes second identification information, the third network device can determine, based on the identification information for the first random access preamble and the information regarding the first time-frequency position, or based on the second identification information, that the first TA indicated by the ninth message corresponds to the first network device to which the first source cell belongs, and can transmit the ninth message to the first network device.

[0271] Similarly, when the ninth message indicates a second TA, if the third information includes identification information and information about the second time-frequency position of the second random access preamble, or if the third information includes fourth identification information, the third network device may determine, based on the identification information and information about the second time-frequency position of the second random access preamble, or based on the fourth identification information, that the second TA indicated by the ninth message corresponds to the fourth network device to which the second source cell belongs, and may transmit the ninth message to the fourth network device.

[0272] When the ninth message indicates a third TA, if the third information includes identification information for a third random access preamble and information regarding a third time-frequency position, or if the third information includes fourth identification information, the third network device may determine, based on the identification information for a third random access preamble and information regarding a third time-frequency position, or based on the fourth identification information, that the third TA indicated by the ninth message corresponds to the fourth network device to which the second source cell belongs, and may transmit the ninth message to the fourth network device.

[0273] S1004: The first network device transmits the first TA to the first terminal device based on the third information, the fourth network device transmits the second TA to the second terminal device based on the third information, or the fourth network device transmits the third TA to the third terminal device based on the third information.

[0274] In this embodiment of the present application, when the ninth message indicates the first TA, the first network device can determine whether the third information in the ninth message matches information about a first resource provided to the first terminal device, such as identification information for a first random access preamble, information about a first time-frequency position, second identification information, or first identification information. If the third information in the ninth message matches information about a first resource provided to the first terminal device, the first network device can determine that the first TA indicated by the ninth message corresponds to the first terminal device and can transmit the first TA to the first terminal device.

[0275] Alternatively, if the third piece of information in the ninth message includes identification information for the first terminal device, the first network device may determine that the first TA indicated by the ninth message corresponds to the first terminal device and transmit the first TA to the first terminal device.

[0276] Similarly, when the ninth message indicates the second TA, the fourth network device can determine whether the third information in the ninth message matches information about the sixth resource provided to the second terminal device, such as the identification information of the second random access preamble, the information about the second time-frequency position, the fourth identification information, and the third identification information. If the third information in the ninth message matches information about the sixth resource provided to the second terminal device, the fourth network device can determine that the second TA indicated by the ninth message corresponds to the second terminal device and can transmit the second TA to the second terminal device.

[0277] Alternatively, if the third piece of information in the ninth message includes identification information for the second terminal device, the fourth network device may determine that the second TA indicated by the ninth message corresponds to the second terminal device and transmit the second TA to the second terminal device.

[0278] When the ninth message indicates the third TA, the fourth network device can determine whether the third information in the ninth message matches information about the seventh resource provided to the third terminal device, such as the identification information of the third random access preamble, the information about the third time-frequency position, the fifth identification information, and the third identification information. If the third information in the ninth message matches information about the seventh resource provided to the third terminal device, the fourth network device can determine that the third TA indicated by the ninth message corresponds to the third terminal device and can transmit the third TA to the third terminal device.

[0279] Alternatively, when the third information in the ninth message includes the identification information of the third terminal device, the fourth network device may determine that the third TA indicated by the ninth message corresponds to the third terminal device, and transmit the third TA to the third terminal device.

[0280] To implement the functions of the foregoing embodiments, it should be understood that the network device and the terminal device include corresponding hardware structures and / or software modules for executing the functions. Those skilled in the art should easily recognize that this application can be implemented in the form of hardware or a combination of hardware and computer software by referring to the units and method steps in the examples described in the embodiments disclosed in this application. Whether the function is executed by hardware or by hardware driven by computer software depends on the specific application scenario of the technical solution and the design constraints.

[0281] FIG. 13 is a diagram of the structure of a possible communication device according to an embodiment of the present application. The communication device may be configured to implement the functions of the network device or the terminal device in the foregoing method embodiments, and thus can also implement the beneficial effects of the foregoing method embodiments. In the present embodiment of the present application, the communication device may be the network device shown in FIG. 1, or the terminal device shown in FIG. 1, or a module (for example, a chip) used in the network device or the terminal device.

[0282] As shown in FIG. 13, the communication device 1300 includes a processing unit 1310 and a transceiver unit 1320. The processing unit 1310 is configured to control the transceiver unit 1320 to implement the functions of the network device or the terminal device in the foregoing method embodiments. The terminal device may be the first terminal device, the second terminal device, or the third terminal device. The network device may be the first network device, the second network device, the third network device, or the fourth network device.

[0283] For example, when the communication device 1300 is configured to implement the functions of the first network device in the foregoing method embodiments, the transceiver unit 1320 is configured to receive a first message from the second network device, the first message indicates a first TA, the first message includes first information, the first information includes identification information of a first random access preamble and information regarding a first time-frequency position for transmitting the first random access preamble, or identification information of a first terminal device, or identification information of a first random access preamble, information regarding a first time-frequency position, and identification information of a first terminal device, and the transceiver unit 1320 is also configured to transmit the first TA to the first terminal device based on the first information.

[0284] For example, if the communication device 1300 is configured to implement the functions of the second network device in the embodiment of the method described above, the transceiver unit 1320 is configured to receive a first random access preamble from a first terminal device and to transmit a first message to the first network device, wherein the first message indicates a first TA, and the first message includes first information, the first information including identification information for the first random access preamble and information regarding a first time-frequency position for transmitting the first random access preamble, or identification information for the first terminal device, or identification information for the first random access preamble and information regarding a first time-frequency position and identification information for the first terminal device. Alternatively, the transceiver unit 1320 is configured to receive a first random access preamble from a first terminal device. A fifth message is sent to a third network device, the fifth message indicates a first TA, the fifth message includes second information, the second information indicates that the first TA corresponds to a first network device to which the first source cell of a first terminal device belongs, and the second information includes identification information for a first random access preamble and information about a first time-frequency position for transmitting the first random access preamble, or second identification information, or identification information for a first random access preamble and information about a first time-frequency position and second identification information.

[0285] For example, when the communication device 1300 is configured to implement the functions of the third network device in the embodiment of the method described above, the transceiver unit 1320 is configured to receive a fifth message from the second network device, the fifth message indicating a first TA, the fifth message including second information, the second information including identification information for a first random access preamble and information regarding a first time-frequency position for transmitting the first random access preamble, or second identification information, or identification information for a first random access preamble and information regarding a first time-frequency position and second identification information, and the transceiver unit 1320 is also configured to transmit a fifth message to the first network device based on the second information.

[0286] For a more detailed description of the processing unit 1310 and the transceiver unit 1320, please refer directly to the relevant description of the embodiment of the method described above. Details will not be repeated here.

[0287] Figure 14 is a diagram of the structure of another possible communication device according to one embodiment of the present application. The communication device 1400 comprises a processor 1410 and an interface circuit 1420. The processor 1410 and the interface circuit 1420 are coupled to each other. It will be understood that the interface circuit 1420 may be a transceiver or an input / output interface. Optionally, the communication device 1400 may further include a memory 1430, which is configured to store instructions performed by the processor 1410, or input data required by the processor 1410 to execute instructions, or data generated after the processor 1410 has executed instructions.

[0288] When the communication device 1400 is configured to implement the method in the embodiment of the method described above, the processor 1410 is configured to implement the functions of the processing unit 1310, and the interface circuit 1420 is configured to implement the functions of the transceiver unit 1320.

[0289] If the communication device is a chip used in a terminal device, the chip within the terminal device implements the functions of the terminal device in the embodiment of the method described above. The chip within the terminal device receives information from another module within the terminal device (e.g., a radio frequency module or an antenna), and the information is transmitted to the terminal device by the network device. Alternatively, the chip within the terminal device transmits information to another module within the terminal device (e.g., a radio frequency module or an antenna), and the information is transmitted to the network device by the terminal device.

[0290] When the communication device is a module used in a network device, the module within the network device implements the functions of the network device in the embodiments of the method described above. The module within the network device receives information from another module within the network device (e.g., a radio frequency module or antenna), and the information is transmitted to the network device by a terminal device. Alternatively, the module within the network device transmits information to another module within the network device (e.g., a radio frequency module or antenna), and the information is transmitted to the terminal device by the network device. The module within the network device as described herein may be the baseband chip of the network device, or it may be a DU or another module. The DU here may be a DU in an open radio access network (O-RAN) architecture.

[0291] It will be understood that the processor in the embodiments of this application may be a Central Processing Unit (CPU), or may be another general-purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), or another programmable logic device, a transistor logic device, a hardware component, or any combination thereof. The general-purpose processor may be a microprocessor or any conventional processor, etc.

[0292] Based on the same technical concept, one embodiment of the present application further provides a computer-readable storage medium containing a program or instructions. When the program or instructions are executed on the computer, the method of the embodiment of the method described above is performed.

[0293] Based on the same technical concept, one embodiment of this application further provides a computer program product including instructions. When the instructions are executed on a computer, the method of the embodiment of the method described above is performed.

[0294] Those skilled in the art will understand that embodiments of this application may be provided as methods, systems, or computer program products. Accordingly, this application may take the form of hardware-only embodiments, software-only embodiments, or embodiments having a combination of software and hardware. In addition, this application may take the form of a computer program product implemented on one or more computer-usable storage media (including, but not limited to, disk memory, CD-ROM, optical memory, etc.) containing computer-usable program code.

[0295] This application is described with reference to flowcharts and / or block diagrams of the methods, devices (systems), and computer program products described herein. It should be understood that computer program instructions may be used to implement each step and / or block in the flowcharts and / or block diagrams, as well as combinations of steps and / or blocks in the flowcharts and / or block diagrams. These computer program instructions may be provided to a general-purpose computer, a dedicated computer, an embedded processor, or a processor of another programmable data processing device to generate a machine, the instructions executed by the computer or the processor of another programmable data processing device, which generates a machine to implement a specific function in one or more steps of the flowchart and / or one or more blocks of the block diagram.

[0296] These computer program instructions may be stored in computer-readable memory, which can be used to instruct a computer or any other programmable data processing device to operate in a specific manner, and as a result, the instructions stored in computer-readable memory generate an artifact that includes an instruction unit. The instruction unit implements one or more steps in a flowchart and / or one or more blocks in a block diagram.

[0297] Computer program instructions may, alternatively, be loaded onto a computer or another programmable data processing device, thereby executing a series of operations and steps on the computer or other programmable device, resulting in the generation of computer execution processes. Thus, instructions executed on a computer or other programmable device provide steps for implementing a particular function in one or more steps in a flowchart and / or one or more blocks in a block diagram.

[0298] It is clear that a person skilled in the art can make various modifications and changes to this application without departing from the spirit and scope of this application. This application incorporates these modifications and variations, provided that they fall within the scope of the claims of this application and the equivalent art thereto. [Explanation of Symbols]

[0299] 1300 Communication equipment 1310 Processing Unit 1320 Transmitter / Receiver Unit 1400 Communication equipment 1410 Processor 1420 Interface Circuit 1430 memory

Claims

1. A timing advance acquisition method applied to a first network device, wherein the first network device is a network device to which a first source cell of a first terminal device belongs, and the method is A step of receiving a first message from a second network device, wherein the second network device is a network device to which at least one candidate cell of the first terminal device belongs, the first message indicates a first timing advance TA, the first message includes first information, and the first information is A receiving step including identification information for a first random access preamble and information regarding a first time-frequency position for transmitting the first random access preamble, or identification information for a first terminal device, or the identification information for the first random access preamble and the information regarding the first time-frequency position and the identification information for the first terminal device, The steps include: transmitting the first TA to the first terminal device based on the first information; Methods that include...

2. Before receiving the first message from the second network device, the method, The step of sending a second message to the first terminal device, wherein the second message instructs the first terminal device to perform uplink synchronization with the second network device, and the second message contains the following information, namely: The identification information and the information relating to the first time-frequency position of the first random access preamble, or Information regarding the first beam direction used to determine the first time-frequency position. Steps including one or more of the following The method according to claim 1, further comprising:

3. The step of transmitting the first TA to the first terminal device based on the first information is: A step of determining, based on the first information, that the first TA corresponds to the first terminal device, The steps include transmitting the first TA to the first terminal device and The method according to claim 1 or 2, including the method described in claim 1 or 2.

4. The information relating to the first time-frequency position is the following information, namely, Identification information for random access channel occasions, Information regarding temporary identifiers for random access wireless networks, or System frame number instruction information, which indicates at least one bit value of the system frame number, The method according to any one of claims 1 to 3, comprising one or more of the above.

5. The method according to any one of claims 1 to 4, wherein the first information further includes first identification information, the first identification information indicates a first target cell of the first terminal device or the second network device, and the first target cell is one of the at least one candidate cell.

6. Before sending the second message to the first terminal device, the method, A step of receiving a third message from the second network device, wherein the third message indicates a first resource in at least one candidate cell, and the first resource is used by a terminal device in the first source cell to perform uplink synchronization with the second network device. The method according to claim 2, further comprising:

7. The aforementioned method, A step of determining a second resource from the first resource, wherein the second resource is used by the first terminal device to perform uplink synchronization with the second network device, and the information relating to the second resource is the following information, namely: The identification information and the information relating to the first time-frequency position of the first random access preamble, or The information relating to the first beam direction, Steps including one or more of the following The method according to claim 6, further comprising:

8. Before receiving the third message from the second network device, the method, A step of sending a fourth message to the second network device, wherein the fourth message is used to request the first resource, and the fourth message includes information about the amount of the first resource. The method according to claim 6 or 7, further comprising:

9. The fourth message above contains the following information, namely, First identification information indicating a first target cell of the first terminal device or the second network device, wherein the first target cell is one of the at least one candidate cell, or Second identification information indicating the first source cell or the first network device, The method according to claim 8, further comprising one or more of the following.

10. The first network device is a first distributed unit DU belonging to a first central unit CU, and the second network device is a second DU belonging to the first CU, and messages are transmitted between the first network device and the second network device via the first CU, or The method according to any one of claims 1 to 9, wherein the first network device is a first DU belonging to a first CU, and the second network device is a second DU belonging to a second CU, and messages are transmitted between the first network device and the second network device via the first CU and the second CU.

11. A timing advance acquisition method applied to a second network device, wherein the second network device is a network device to which at least one candidate cell of a first terminal device belongs, and the method is The steps include receiving a first random access preamble from the first terminal device, A step of sending a first message to a first network device, wherein the first network device is a network device to which the first source cell of the first terminal device belongs, the first message indicates a first TA, the first message includes first information, the first information indicates that the first TA corresponds to the first terminal device, and the first information is A step comprising: identification information of the first random access preamble and information regarding a first time-frequency position for transmitting the first random access preamble, or identification information of the first terminal device, or the identification information of the first random access preamble and the information regarding the first time-frequency position and the identification information of the first terminal device. Methods that include...

12. The information relating to the first time-frequency position is the following information, namely, Identification information for random access channel occasions, Information regarding temporary identifiers for random access wireless networks, or System frame number instruction information, which indicates at least one bit value of the system frame number, The method according to claim 11, comprising one or more of the above.

13. The method according to claim 11 or 12, wherein the first information further includes first identification information, the first identification information indicates a first target cell of the first terminal device or the second network device, and the first target cell is one of the at least one candidate cell.

14. Before receiving the first random access preamble from the first terminal device, the method: A step of sending a third message to the first network device, wherein the third message indicates a first resource of at least one candidate cell, and the first resource is used by a terminal device in the first source cell to perform uplink synchronization with the second network device. The method according to any one of claims 11 to 13, further comprising:

15. Before sending the third message to the first network device, the method, A step of receiving a fourth message from the first network device, wherein the fourth message is used to request the first resource, and the fourth message includes information regarding the amount of the first resource. The method according to claim 14, further comprising:

16. The fourth message above contains the following information, namely, The first identification information indicating the first target cell of the first terminal device or the second network device, wherein the first target cell is one of the at least one candidate cell, or Second identification information indicating the first source cell or the first network device, The method according to claim 15, further comprising one or more of the following.

17. The first information includes the identification information of the first terminal device, and before sending the first message to the first network device, the method Step of receiving the identification information of the first terminal device from the first terminal device. The method according to any one of claims 11 to 16, further comprising:

18. The first network device is a first DU belonging to the first CU, and the second network device is a second DU belonging to the first CU, and messages are transmitted between the first network device and the second network device via the first CU, or The method according to any one of claims 11 to 17, wherein the first network device is a first DU belonging to a first CU, and the second network device is a second DU belonging to a second CU, and messages are transmitted between the first network device and the second network device via the first CU and the second CU.

19. A timing advance acquisition method applied to a second network device, wherein the second network device is a network device to which at least one candidate cell of a first terminal device belongs, and the method is The steps include receiving a first random access preamble from a first terminal device, A step of sending a fifth message to a third network device, wherein the fifth message indicates a first TA, the fifth message includes second information, the second information indicates that the first TA corresponds to a first network device to which the first source cell of the first terminal device belongs, A step comprising: identification information for the first random access preamble and information regarding a first time-frequency position for transmitting the first random access preamble, or second identification information indicating the first source cell or the first network device, or the identification information for the first random access preamble and the information regarding the first time-frequency position and the second identification information. Methods that include...

20. The information relating to the first time-frequency position is the following information, namely, Identification information for random access channel occasions, Information regarding temporary identifiers for random access wireless networks, or System frame number instruction information, which indicates at least one bit value of the system frame number, The method according to claim 19, comprising one or more of the above.

21. Before receiving the first random access preamble from the first terminal device, the method: A step of sending a sixth message to the third network device, wherein the sixth message indicates a fourth resource of at least one candidate cell, the fourth resource is used by the first source cell and terminal devices in the second source cell of the second terminal device to perform uplink synchronization with the second network device, and the network device to which the second source cell belongs is the fourth network device. The method according to claim 19 or 20, further comprising:

22. Before sending the sixth message to the third network device, the method, A step of receiving a seventh message from the third network device, wherein the seventh message is used to request the fourth resource, and the seventh message includes information regarding the amount of the fourth resource. The method according to claim 21, further comprising:

23. The seventh message above contains the following information, namely, First identification information indicating a first target cell of the first terminal device or the second network device, wherein the first target cell is one of the at least one candidate cell, The second identification information, Third identification information indicating a second target cell of the second terminal device or the second network device, wherein the second target cell is one of the at least one candidate cell, or A fourth identification piece indicating the second source cell, The method according to claim 22, further comprising one or more of the above.

24. Before sending the sixth message to the third network device, the method, A step of determining a first resource and a fifth resource from the fourth resource, wherein the first resource is used by the terminal device in the first source cell to perform uplink synchronization with the second network device, the fifth resource is used by the terminal device in the second source cell to perform uplink synchronization with the second network device, and the first resource is different from the fifth resource. The method according to claim 23, further comprising:

25. The second information includes the second identification information, and after receiving the first random access preamble from the first terminal device, the method Steps to determine the second identification information based on the first random access preamble and the first resource. The method according to claim 24, including the method described in claim 24.

26. The third network device is the first CU, the first network device is the first DU belonging to the first CU, the second network device is the second DU belonging to the first CU, and messages are transmitted between the first network device and the second network device via the first CU, or The method according to any one of claims 19 to 25, wherein the third network device is a second CU, the first network device is a first DU belonging to the first CU, the second network device is a second DU belonging to the second CU, and messages are transmitted between the first network device and the second network device via the first CU and the second CU.

27. A timing advance acquisition method applicable to a third network device, wherein the method is: The step of receiving a fifth message from a second network device, wherein the second network device is a network device to which at least one candidate cell of the first terminal device belongs, the fifth message indicates the first TA, the fifth message includes second information, and the second information is A receiving step including identification information for the first random access preamble and information regarding a first time-frequency position for transmitting the first random access preamble, or second identification information indicating a first source cell of the first terminal device or a first network device to which the first source cell belongs, or the identification information for the first random access preamble and the information regarding the first time-frequency position and the second identification information, The steps include sending the fifth message to the first network device based on the second information, and Methods that include...

28. The step of sending the fifth message to the first network device based on the second information is: Based on the second information, the first TA determines that it corresponds to the first network device, The steps include sending the fifth message to the first network device and The method according to claim 27, including the method described in claim 27.

29. The information relating to the first time-frequency position is the following information, namely, Identification information for random access channel occasions, Information regarding temporary identifiers for random access wireless networks, or System frame number instruction information, which indicates at least one bit value of the system frame number, The method according to claim 27 or 28, comprising one or more of the above.

30. Before receiving the fifth message from the second network device, the method, The step of receiving a sixth message from the second network device, wherein the sixth message indicates a fourth resource of at least one candidate cell, the fourth resource is used by the first source cell and terminal devices in the second source cell of the second terminal device to perform uplink synchronization with the second network device, and the network device to which the second source cell belongs is the fourth network device. A step of determining a first resource and a fifth resource from the fourth resource, wherein the first resource is used by the terminal device in the first source cell to perform uplink synchronization with the second network device, the fifth resource is used by the terminal device in the second source cell to perform uplink synchronization with the second network device, and the first resource is different from the fifth resource. A step of sending an eighth message to the first network device, wherein the eighth message indicates the first resource. The method according to any one of claims 27 to 29, further comprising:

31. The method according to claim 30, wherein the first resource is a resource corresponding to a first bandwidth portion BWP of the at least one candidate cell, and the fifth resource is a resource corresponding to a second BWP of the at least one candidate cell.

32. The method according to claim 31, wherein the second information further includes identification information of the first BWP.

33. Before receiving the sixth message from the second network device, the method, Steps include sending a seventh message to the second network device, wherein the seventh message is used to request the fourth resource, and the seventh message includes information regarding the amount of the fourth resource. The method according to any one of claims 30 to 32, further comprising:

34. The seventh message above contains the following information, namely, First identification information indicating a first target cell of the first terminal device or the second network device, wherein the first target cell is one of the at least one candidate cell, The second identification information, Third identification information indicating a second target cell of the second terminal device or the second network device, wherein the second target cell is one of the at least one candidate cell, or A fourth identification piece indicating the second source cell, The method according to claim 33, further comprising one or more of the following.

35. The third network device is the first CU, the first network device is the first DU belonging to the first CU, the second network device is the second DU belonging to the first CU, and messages are transmitted between the first network device and the second network device via the first CU, or The method according to any one of claims 27 to 34, wherein the third network device is a second CU, the first network device is a first DU belonging to the first CU, the second network device is a second DU belonging to the second CU, and messages are transmitted between the first network device and the second network device via the first CU and the second CU.

36. A timing advance acquisition method applied to a first network device, wherein the first network device is a network device to which a first source cell of a first terminal device belongs, and the method is A step of transmitting the first switch command to the first terminal device, wherein the first switch command includes the TA field, and if the value of the TA field is a first value, the first value is The first network device indicates one or more of the following: the first network device fails to acquire a first TA, the first TA is invalid, or the first terminal device accesses a second network device via random access, wherein the second network device is a network device to which at least one candidate cell of the first terminal device belongs. Methods that include...

37. The method according to claim 36, wherein the TA field includes m binary bits, and when the value of the TA field is the first value, all m binary bits are set to 1, and m is a positive integer.

38. The method according to claim 36 or 37, wherein when the value of the TA field is a second value, the second value indicates that the first TA is valid.

39. This is a method for obtaining Timing Advance, The steps of receiving a first switch command from a first network device, wherein the first switch command includes a TA field, and the first network device is a network device to which the first source cell of a first terminal device belongs. If the value of the TA field is a first value, then based on the first value, A step of determining one or more of the following: the first network device fails to acquire a first TA, the first TA is invalid, or the first terminal device accesses a second network device via random access, wherein the second network device is a network device to which at least one candidate cell of the first terminal device belongs. Methods that include...

40. The method according to claim 39, wherein the TA field includes m binary bits, and when the value of the TA field is the first value, all m binary bits are set to 1, and m is a positive integer.

41. The method according to claim 39 or 40, wherein when the value of the TA field is a second value, the first TA is determined to be valid based on the second value.

42. A communication device comprising: a module configured to perform the method described in any one of claims 1 to 10; a module configured to perform the method described in any one of claims 11 to 18; a module configured to perform the method described in any one of claims 19 to 26; a module configured to perform the method described in any one of claims 27 to 35; a module configured to perform the method described in any one of claims 36 to 38; or a module configured to perform the method described in any one of claims 39 to 41.

43. A communication device comprising a processor and an interface circuit, wherein the interface circuit is configured to receive a signal from another communication device different from the communication device and transmit the signal to the processor, or transmit a signal from the processor to another communication device different from the communication device, and the processor is configured to implement the method according to any one of claims 1 to 10, any one of claims 11 to 18, any one of claims 19 to 26, any one of claims 27 to 35, any one of claims 36 to 38, or any one of claims 39 to 41 via logic circuits or by executing code instructions.

44. A computer-readable storage medium comprising a program or instruction, wherein when the program or instruction is executed on a computer, the method according to any one of claims 1 to 10 is performed, the method according to any one of claims 11 to 18 is performed, the method according to any one of claims 19 to 26 is performed, the method according to any one of claims 27 to 35 is performed, the method according to any one of claims 36 to 38 is performed, or the method according to any one of claims 39 to 41 is performed.

45. A computer program product comprising a computer program, wherein when the computer program is executed by a communication device, the method according to any one of claims 1 to 10 is implemented, the method according to any one of claims 11 to 18 is implemented, the method according to any one of claims 19 to 26 is implemented, the method according to any one of claims 27 to 35 is implemented, the method according to any one of claims 36 to 38 is implemented, or the method according to any one of claims 39 to 41 is implemented.

46. A communication system comprising a first network device, a second network device, a third network device, and a first terminal device, wherein the first network device is configured to implement the method according to any one of claims 1 to 10 or any one of claims 36 to 38, the second network device is configured to implement the method according to any one of claims 11 to 18 or any one of claims 19 to 26, the third network device is configured to implement the method according to any one of claims 27 to 35, and the first terminal device is configured to implement the method according to any one of claims 39 to 41.

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